query: Fix artist and album search return all songs

Searching for artist/album returned all songs.
Changed sparql where_clause to return songs only specific
to the album/artist/composer searched.

Fixes GNOME/gnome-music#4
3 jobs for patch-1 in 25 minutes and 12 seconds (queued for 3 minutes and 6 seconds)
latest
Status Job ID Name Coverage
  Check
passed #6335
pep8

00:06:15

passed #6334
pyflakes

00:06:22

 
  Build
passed #6336
build

00:12:34