Fix loading of fonts with empty font files (bug 866395 and issue 3522)

[Snuffleupagus]

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=866395.
Fixes #3522.

I've struggled with the best way to create the isEmpty property for the DecodeStream. The first idea, to check if peekBytes(1) returns data won't work at the end of the stream. Furthermore just checking if this.buffer is null or empty won't work either, because if ensureBuffer has been called that no longer holds even if the stream was actually empty. The only remaining (simple) approach seem to be to read enough of the stream and then check if this.bufferLength === 0, since that should only happen when the stream is actually empty.

If the current approach used in this PR isn't any good, we might instead do something along these lines:

get isEmpty() {
  if (this.pos === 0) {
    return (this.peekBytes(1).length === 0);
  }
  var currentPos = this.pos;
  this.reset();
  var firstByte = this.peekBytes(1);
  this.skip(currentPos);
  return (firstByte.length === 0);
}

@yurydelendik Which solution do you prefer?

[yurydelendik]

nit: if (file) { will look as good

[yurydelendik]

I think it looks good now. Could you add one isEmpty to the https://github.com/mozilla/pdf.js/blob/master/src/core/chunked_stream.js ?

[Snuffleupagus]

Done, done and done; thanks for the very quick review!

/botio test

[pdfjsbot]

From: Bot.io (Windows)

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Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://107.22.172.223:8877/dd69a61069a4f0f/output.txt

[pdfjsbot]

From: Bot.io (Linux)

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Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://107.21.233.14:8877/7481e1ac1fcc1a1/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Failed

Full output at http://107.22.172.223:8877/dd69a61069a4f0f/output.txt

Total script time: 2.81 mins

• Font tests: FAILED
• Unit tests: Passed
• Regression tests: FAILED

Image differences available at: http://107.22.172.223:8877/dd69a61069a4f0f/reftest-analyzer.html#web=eq.log

[pdfjsbot]

From: Bot.io (Linux)

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Success

Full output at http://107.21.233.14:8877/7481e1ac1fcc1a1/output.txt

Total script time: 25.99 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[yurydelendik]

/botio-windows test

[pdfjsbot]

From: Bot.io (Windows)

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Received

Command cmd_test from @yurydelendik received. Current queue size: 0

Live output at: http://107.22.172.223:8877/1c67e0381b4251e/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Success

Full output at http://107.22.172.223:8877/1c67e0381b4251e/output.txt

Total script time: 23.60 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[yurydelendik]

/botio makeref

[pdfjsbot]

From: Bot.io (Linux)

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Received

Command cmd_makeref from @yurydelendik received. Current queue size: 0

Live output at: http://107.21.233.14:8877/da6ef04bf008ec7/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Received

Command cmd_makeref from @yurydelendik received. Current queue size: 0

Live output at: http://107.22.172.223:8877/c7974e8012af51c/output.txt

[yurydelendik]

Thank you for the patch

[pdfjsbot]

From: Bot.io (Windows)

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Success

Full output at http://107.22.172.223:8877/c7974e8012af51c/output.txt

Total script time: 23.87 mins

• Lint: Passed
• Make references: Passed
• Check references: Passed

[pdfjsbot]

From: Bot.io (Linux)

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Success

Full output at http://107.21.233.14:8877/da6ef04bf008ec7/output.txt

Total script time: 26.25 mins

• Lint: Passed
• Make references: Passed
• Check references: Passed