Fixed problem where albums with secondary types still got added

So this is my own response to issue #1372.
I have no experience with Python whatsoever, so it took me ages :P
Albums with Secondary type DJ-Mix get shown as a normal Album in the Musicbrainz XML. So I changed 1 single line to check wether an album has a secondary type, and if so, to skip it.
I checked if the extra's feature still works and it seems fine.