fix the compilation album insertion
Summary:
partial fix for handling albums without album artist
partially handle the case of compilations not getting Various Artists as
album artist
BUG: 409147
Test Plan: all tests are fine and most common cases should be covered.
Reviewers: Elisa, ngraham, astippich
Reviewed By: Elisa, ngraham
Differential Revision: https://phabricator.kde.org/D22499