MythMusic: Fix detection of compilations using special MusicBrainz Artist ID

Look at all the fields in the 'TXXX=MusicBrainz Album Artist Id' frame for the special
various artists ID not just the first one which in current version of the taglib
contains the tags description.

Refs #10235.
Fixes #12000.

(cherry picked from commit 6530ac633300a32c76db0d10cf8d107aa712a62c)