Allow to rename the extension

[LeoNoBit]

Greetings. Currently from the filename field it displays and allows you to edit the file extension, however when you make any changes the extension is simply duplicated.

That is, if you try to rename song.flac to song.flac.bak, you will get song.flac.bak.flac.

This behavior is not really useful or expected (for that purpose it would be better not to allow editing), and another problem is that it is not even shown until the file is reloaded.
I would like to request that the extension be allowed to be freely renamed.