move_art: Remove missing album art

[projectgus]

Prevents a fatal file system error on "beet update" if the album art file has been moved or renamed
and the beets library hasn't been updated with the new path.

[sampsyo]

Interesting idea! This could help remove a common pain point. Have you tried this out fairly thoroughly? It seems innocuous enough, but this is a pretty sensitive path in common workflows, so it would be awesome to make sure we're not doing anything unexpected.

[projectgus]

Hi @sampsyo ,

Good question! I've only tested this in my own library. A while ago I used a script to rename a bunch of cover files to folder.jpg (to keep Android happy), and after that beet update would crash with a filesystem error. After this change, the next beet update removed the stale cover art entries and I could continue.

I'm not sure that this is the best place in the code to be cleaning up this metadata in the library, but I couldn't find a better place...

An alternative change would be just to log that the file doesn't exist here and keep going (rather than quit with a fatal error). However I wasn't sure it's possible for a user to easily fix broken cover art links in another way, so clearing the entry at the same time seemed like a win/win. Happy to change it if you prefer, though.

[sampsyo]

Alright; thanks! I think we should go for it. Could you please add a changelog entry?

Also, may I suggest this slightly more direct wording for the error log?

removing reference to missing album art file {}

[projectgus]

@sampsyo Sure thing, done and done!

[sampsyo]

Awesome; thank you! Merged. ✨