AIFF: Fix handling of padding bytes, safe chunk manipulation

[phw]

This refactors the AIFF code to:

• Fix handling of padding bytes: For chunks with odd data size there must be a padding byte added. This is now consistently handled for all chunk manipulation (resize, insert, delete). Previously this was not handled for all cases, and reading a file which had a ID3 chunk with padding could lead to file corruption since mutagen would write this chunk back with an even size but keep the padding byte.
• The code can now safely support multiple chunk insert / resize / delete operations while keeping the in-memory representation of all offsets and sizes intact. Previously it was not safe to e.g. both insert and delete chunks in a loaded file, since the in-memory stored offsets for chunks were not updated. This lead to file corruption since data was manipulated at the wrong location

See also the same changes for RIFF files in #408

[phw]

@lazka Any chance to get this fix included in a new release in the not too far future?

This issue actually is rather bad, I'm thinking about disabling AIFF tag writing in Picard for mutagen versions affected by this, but it would be good to have a fixed version available then.

[lazka]

I'll look into it this weekend.

[lazka]

puh, a bit hard to review with everything mixed together :/ so I'm just going to click merge here

[lazka]

1.43.0 is out

[evanpurkhiser]

Thanks for fixing this @phw. That was some of the first low-level-file code I had written 🙂