Tasks: Fix playlist linking task cleanup
Tasks: Fix playlist linking task cleanup

This fixes a potential constraint violation when trying to insert new
linking task for an unprocessed playlist
Missing bits from 889932819f94f03a6c3b5bec89769cb1401967bc

chouquette/medialibrary,chouquette/medialibrary,chouquette/medialibrary,chouquette/medialibrary