Removing a connection causes a panic sometimes

[vladbat00]

I can't always reproduce it, it's probably some kind of a race condition.

thread 'IO Task Pool (0)' panicked at 'called `Option::unwrap()` on a `None` value', /Users/mvlabat/.cargo/registry/src/garden.eu.org-1ecc6299db9ec823/bevy_networking_turbulence-0.3.3/src/transport.rs:209:55
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic
   3: core::option::Option<T>::unwrap
             at /rustc/59216858a323978a97593cba22b5ed84350a3783/library/core/src/option.rs:722:21
   4: <bevy_networking_turbulence::transport::ServerConnection as bevy_networking_turbulence::transport::Connection>::build_channels::{{closure}}
             at /Users/mvlabat/.cargo/registry/src/garden.eu.org-1ecc6299db9ec823/bevy_networking_turbulence-0.3.3/src/transport.rs:209:30
   5: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
             at /rustc/59216858a323978a97593cba22b5ed84350a3783/library/core/src/future/mod.rs:80:19
   6: async_executor::Executor::spawn::{{closure}}
             at /Users/mvlabat/.cargo/registry/src/garden.eu.org-1ecc6299db9ec823/async-executor-1.4.1/src/lib.rs:144:13
   7: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
             at /rustc/59216858a323978a97593cba22b5ed84350a3783/library/core/src/future/mod.rs:80:19
   8: async_task::raw::RawTask<F,T,S>::run
             at /Users/mvlabat/.cargo/registry/src/garden.eu.org-1ecc6299db9ec823/async-task-4.0.3/src/raw.rs:489:20
   9: async_executor::Executor::run::{{closure}}::{{closure}}
             at /Users/mvlabat/.cargo/registry/src/garden.eu.org-1ecc6299db9ec823/async-executor-1.4.1/src/lib.rs:235:21
  10: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
             at /rustc/59216858a323978a97593cba22b5ed84350a3783/library/core/src/future/mod.rs:80:19
  11: <futures_lite::future::Or<F1,F2> as core::future::future::Future>::poll
             at /Users/mvlabat/.cargo/registry/src/garden.eu.org-1ecc6299db9ec823/futures-lite-1.12.0/src/future.rs:529:33
  12: async_executor::Executor::run::{{closure}}
             at /Users/mvlabat/.cargo/registry/src/garden.eu.org-1ecc6299db9ec823/async-executor-1.4.1/src/lib.rs:242:9
  13: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
             at /rustc/59216858a323978a97593cba22b5ed84350a3783/library/core/src/future/mod.rs:80:19
  14: futures_lite::future::block_on::{{closure}}
             at /Users/mvlabat/.cargo/registry/src/garden.eu.org-1ecc6299db9ec823/futures-lite-1.12.0/src/future.rs:89:27
  15: std::thread::local::LocalKey<T>::try_with
             at /rustc/59216858a323978a97593cba22b5ed84350a3783/library/std/src/thread/local.rs:399:16
  16: std::thread::local::LocalKey<T>::with
             at /rustc/59216858a323978a97593cba22b5ed84350a3783/library/std/src/thread/local.rs:375:9
  17: futures_lite::future::block_on
             at /Users/mvlabat/.cargo/registry/src/garden.eu.org-1ecc6299db9ec823/futures-lite-1.12.0/src/future.rs:79:5
  18: bevy_tasks::task_pool::TaskPool::new_internal::{{closure}}::{{closure}}
             at /Users/mvlabat/.cargo/git/checkouts/_empty-a49bea87237abba3/5a3e28a/crates/bevy_tasks/src/task_pool.rs:139:25