media-db: Return empty result on unknown criteria
media-db: Return empty result on unknown criteria

Tarnyko/rygel,luisbg/rygel,GNOME/rygel,GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,GNOME/rygel,jku/rygel,jku/rygel,Pelagicore/Media-Manager-Rygel-patched,Tarnyko/rygel,Pelagicore/Media-Manager-Rygel-patched