[musicdb] fix album & artist lt operators, used for set/map (e.g. cache)
[musicdb] fix some problems with non-musicbrainz albums in scanner, and tidy up some of the scanner overall.
[musicdb] fix album and artist SQL queries for musicbrainz
Merge pull request #2974 from night199uk/musicfixes

[musicdb] Fixes for non-MusicBrainz albums