Enable support for the `*.m4b` extension

[sonicnkt]

Hi, could you also support the extension m4b? It is just an m4a (aac) audio file with a b instead of a that marks it as an audiobook file. If i rename on of my files to m4a it works fine in tagger.

Probably only needs those two files to me modified slightly but i don't want to mess with cpp code ;) https://github.com/nlogozzo/NickvisionTagger/search?q=m4a

[nlogozzo]

https://github.com/nlogozzo/NickvisionTagger/releases/tag/2022.11.1-f1

Should be available on Flathub in a few hours.

[sonicnkt]

Thanks a lot ;)