Fix duration not showing for tracks not in database
Currently tracks which are not in database return QTime of 00:00:00, which shows up in Tracks list. The only way to fix this, we need to scan the files that lack databaseId for their duration.
Possible issues: If the music files are stored on a disk that is slow, spun down or remote, the scanning of files could worsen the performance (Though baloo most likely has already woken up the disks to track changes). Obviously this is a band-aid fix to the fact that we don't insert all tracks into the database, and this could be removed when the database version is upgraded and the issue is fixed.
Please review if this is a sane fix.