scanner: accept thumbnail images that use the dir name

[coderobe]

some album releases have their covers shipped as "Artist - Album/Artist - Album.png", this includes such

[coderobe]

turns out that this doesn't work when there's a track in the album with the same name as the album itself (such as your test cases, which is why CI fails)

this should probably check for image filetypes somehow?

[coderobe]

also, if it does eventually check for image filetypes perhaps it should add the first image that is not already covered as thumbnail stem as thumbnail when no alternative can be found, as some albums might be structured like such: Artist - Album (2001) [FLAC]/Artist - Album.jpg, where the thumbnail is the name of the album, but the dirname has additional qualifiers added to it. if that is the case but a thumbnail stem (i.e. thumbnail.png) can also be found in the dir, the thumbnail stem should win of course

[boreq]

@coderobe
Given the recent updates to the way thumbnail detection works I think it should now be easy to make this pull request work. The new scanner config fields such as ThumbnailExtensions could be used together with the parent album name.