Fixes to mp4 parsing

[mlrsmith]

Two fixes (separate commits):

• Handle trailing four-byte terminator in VisualSampleEntryBox
• Handle quicktime-style AudioSampleEntryBox variants (and add 'lcpm' handling)

[mlrsmith]

Oops - this was intended as a PR to an internal fork for now, accidentally set the wrong branch base.

Nonetheless, I think these are valuable fixes - let me know if you'd prefer if I split them out to separate PRs.

These all fix failures to parse real-world MP4s (and in the case of the last commit, a crash).

[tobbee]

@mlrsmith Thanks for using the mp4ff library. I'm open to adding support for less common cases as long as the performance is not degraded much for normal usage.

That said, there is an increased maintenance effort with every new tweak, so it is important that there is good testing for them. The way this project is setup now, a GitHub action prohibits merging of a PR into the master branch if the test coverage decreases. This means that all new code must have a test coverage of at least 81% as of now.

If want to provide tests, please make sure that any test files are small, so that the library doesn't grow too much.

[mlrsmith]

Thanks! I'll try to find some time to build test cases that aren't private customer data, and pull the fixes out into separate PRs.

For now, closing this.