Stop server elegantly instead of panic when db closed

[DarianShawn]

Description

The close sequence was not appropriate. It closed the db first, which might be processing block written job. Then close network, etc.

This PR

• Close consensus, network and txpool first, then stop blockchain executor processing block before close the db.
• Removes the panic logic when closed.
• Adds some nil check if we get empty code of a contract address.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Manual tests

• Set up a MainNet node and join the network.
• Stop the server when syncing block. Repeat it several times.

In target branch, we'll get some logs below, which would never happen in the PR branch:

[SIGNAL] Caught signal: interrupt
Gracefully shutting down client...

panic: leveldb: closed

goroutine 157 [running]:
github.com/dogechain-lab/dogechain/state/immutable-trie.(*KVStorage).Get(0x0, {0xc042fb5600, 0xc047fda710, 0xc040e80580})
	/go/src/state/immutable-trie/storage.go:77 +0x96
github.com/dogechain-lab/dogechain/state/immutable-trie.GetNode({0xc042fb5600, 0x41473e5, 0xc047fda7c8}, {0x58acee8, 0xc000588380})
	/go/src/state/immutable-trie/storage.go:155 +0x88
github.com/dogechain-lab/dogechain/state/immutable-trie.(*Txn).lookup(0xc047fdaa60, {0x50a3680, 0xc040e80500}, {0xc0387666e3, 0xc0077bfec0, 0xc000588380})
	/go/src/state/immutable-trie/trie.go:274 +0x1c8
github.com/dogechain-lab/dogechain/state/immutable-trie.(*Txn).lookup(0xc047fdaa60, {0x512dfa0, 0xc0408c88c0}, {0xc0387666e2, 0xc000588380, 0x8})
	/go/src/state/immutable-trie/trie.go:313 +0x2ea
github.com/dogechain-lab/dogechain/state/immutable-trie.(*Txn).lookup(0xc047fdaa60, {0x50a3680, 0xc03d68f560}, {0xc0387666e2, 0x400dd94, 0x0})
	/go/src/state/immutable-trie/trie.go:283 +0x212
github.com/dogechain-lab/dogechain/state/immutable-trie.(*Txn).lookup(0xc047fdaa60, {0x512dfa0, 0xc0500a37c0}, {0xc0387666e1, 0x404ef32, 0x41})
	/go/src/state/immutable-trie/trie.go:313 +0x2ea
github.com/dogechain-lab/dogechain/state/immutable-trie.(*Txn).lookup(0xc047fdaa60, {0x512dfa0, 0xc03d212640}, {0xc0387666e0, 0x10100c047fdaa50, 0x32399218})
	/go/src/state/immutable-trie/trie.go:313 +0x2ea
github.com/dogechain-lab/dogechain/state/immutable-trie.(*Txn).Lookup(0xc047fdaa60, {0xc042fb5560, 0xc00006ed80, 0xc042fb5560})
	/go/src/state/immutable-trie/trie.go:262 +0x5b
github.com/dogechain-lab/dogechain/state/immutable-trie.(*Trie).Get(0xc00edf6b48, {0xc042fb5560, 0x413e370, 0xc00edf6a80})
	/go/src/state/immutable-trie/trie.go:105 +0x74
github.com/dogechain-lab/dogechain/state.(*StateObject).GetCommitedState(0xc00f05bec0, {0x14, 0x7, 0xac, 0x76, 0x1f, 0x93, 0x1f, 0xb7, 0x7a, ...})
	/go/src/state/state.go:131 +0xa4
github.com/dogechain-lab/dogechain/state.(*Txn).GetState(0xc0fa98e1b171005b, {0x10, 0xed, 0x1a, 0x8b, 0x2e, 0x90, 0x8b, 0xdd, 0x45, ...}, ...)
	/go/src/state/txn.go:365 +0x2a8
github.com/dogechain-lab/dogechain/state.(*Transition).GetStorage(0x20, {0x10, 0xed, 0x1a, 0x8b, 0x2e, 0x90, 0x8b, 0xdd, 0x45, ...}, ...)
	/go/src/state/executor.go:826 +0x7a
github.com/dogechain-lab/dogechain/state/runtime/evm.opSload(0xc047145320)
	/go/src/state/runtime/evm/instructions.go:481 +0x16c
github.com/dogechain-lab/dogechain/state/runtime/evm.(*state).Run(0xc047145320)
	/go/src/state/runtime/evm/state.go:245 +0x110
github.com/dogechain-lab/dogechain/state/runtime/evm.(*EVM).Run(0x6737740, 0xc00e58d3f0, {0x58ccde0, 0xc049fd6700}, 0xc049fd6730)
	/go/src/state/runtime/evm/evm.go:45 +0x15f
github.com/dogechain-lab/dogechain/state.(*Transition).run(0xc049fd6700, 0xb7dfd3f7c127e104, {0x58ccde0, 0xc049fd6700})
	/go/src/state/executor.go:632 +0x16f
github.com/dogechain-lab/dogechain/state.(*Transition).applyCall(0xc049fd6700, 0xc00e58d3f0, 0x0, {0x58ccde0, 0xc049fd6700})
	/go/src/state/executor.go:685 +0x2b3
github.com/dogechain-lab/dogechain/state.(*Transition).Callx(0xc039078a20, 0xf1, {0x58ccde0, 0xc049fd6700})
	/go/src/state/executor.go:855 +0x45
github.com/dogechain-lab/dogechain/state/runtime/evm.opCall.func1(0xc039078a20)
	/go/src/state/runtime/evm/instructions.go:1162 +0x2a4
github.com/dogechain-lab/dogechain/state/runtime/evm.(*state).Run(0xc039078a20)
	/go/src/state/runtime/evm/state.go:245 +0x110
github.com/dogechain-lab/dogechain/state/runtime/evm.(*EVM).Run(0x6737740, 0xc00e58d340, {0x58ccde0, 0xc049fd6700}, 0xc049fd6730)
	/go/src/state/runtime/evm/evm.go:45 +0x15f
github.com/dogechain-lab/dogechain/state.(*Transition).run(0xc049fd6700, 0xf4910367dd938a4d, {0x58ccde0, 0xc049fd6700})
	/go/src/state/executor.go:632 +0x16f
github.com/dogechain-lab/dogechain/state.(*Transition).applyCall(0xc049fd6700, 0xc00e58d340, 0x0, {0x58ccde0, 0xc049fd6700})
	/go/src/state/executor.go:685 +0x2b3
github.com/dogechain-lab/dogechain/state.(*Transition).Call2(0xc049fd6700, {0x6e, 0x72, 0xbc, 0x5f, 0x52, 0x40, 0x9a, 0x9d, 0x4d, ...}, ...)
	/go/src/state/executor.go:626 +0x265
github.com/dogechain-lab/dogechain/state.(*Transition).apply(0xc049fd6700, 0xc02ae6b7c0)
	/go/src/state/executor.go:585 +0xd0c
github.com/dogechain-lab/dogechain/state.(*Transition).Apply(0xc049fd6700, 0x6737740)
	/go/src/state/executor.go:394 +0x133
github.com/dogechain-lab/dogechain/state.(*Transition).Write(0xc049fd6700, 0xc010b60d20)
	/go/src/state/executor.go:253 +0x15d
github.com/dogechain-lab/dogechain/state.(*Executor).ProcessBlock(0x51f8520, {0x60, 0xeb, 0x1, 0xc6, 0x95, 0xe6, 0x61, 0x97, 0x38, ...}, ...)
	/go/src/state/executor.go:113 +0x107
github.com/dogechain-lab/dogechain/blockchain.(*Blockchain).executeBlockTransactions(0xc0000d2840, 0xc04c532f00)
	/go/src/blockchain/blockchain.go:847 +0x149
github.com/dogechain-lab/dogechain/blockchain.(*Blockchain).verifyBlockBody(0xc0000d2840, 0xc04c532f00)
	/go/src/blockchain/blockchain.go:792 +0x125
github.com/dogechain-lab/dogechain/blockchain.(*Blockchain).verifyBlock(0xc000f72c60, 0xc04c532f00)
	/go/src/blockchain/blockchain.go:706 +0x3c
github.com/dogechain-lab/dogechain/blockchain.(*Blockchain).VerifyFinalizedBlock(0xc0000d2840, 0xc04c532f00)
	/go/src/blockchain/blockchain.go:685 +0xa7
github.com/dogechain-lab/dogechain/protocol.(*Syncer).BulkSyncWithPeer(0xc00056e300, 0xc01925ea10, 0xc03c20e0c0)
	/go/src/protocol/syncer.go:619 +0x5b8
github.com/dogechain-lab/dogechain/consensus/ibft.(*Ibft).runSyncState(0xc000f72c60)
	/go/src/consensus/ibft/ibft.go:505 +0x144
github.com/dogechain-lab/dogechain/consensus/ibft.(*Ibft).runCycle(0xaf636)
	/go/src/consensus/ibft/ibft.go:440 +0x1dd
github.com/dogechain-lab/dogechain/consensus/ibft.(*Ibft).start(0xc000f72c60)
	/go/src/consensus/ibft/ibft.go:417 +0xe5
created by github.com/dogechain-lab/dogechain/consensus/ibft.(*Ibft).Start
	/go/src/consensus/ibft/ibft.go:221 +0x1c9

[0xcb9ff9]

LGTM