[CoverArtSpec] Support albums without an artist (bgo#612626)
[CoverArtSpec] Support albums without an artist (bgo#612626)

Signed-off-by: Alexander Kojevnikov <e46fc836cca3acec03944314d1457c2ae6c68ef3@kojevnikov.com>

Dynalon/banshee-osx,lamalex/Banshee,Carbenium/banshee,GNOME/banshee,arfbtwn/banshee,ixfalia/banshee,dufoli/banshee,babycaseny/banshee,ixfalia/banshee,stsundermann/banshee,directhex/banshee-hacks,petejohanson/banshee,lamalex/Banshee,ixfalia/banshee,allquixotic/banshee-gst-sharp-work,GNOME/banshee,mono-soc-2011/banshee,GNOME/banshee,ixfalia/banshee,GNOME/banshee,GNOME/banshee,allquixotic/banshee-gst-sharp-work,allquixotic/banshee-gst-sharp-work,babycaseny/banshee,directhex/banshee-hacks,lamalex/Banshee,directhex/banshee-hacks,babycaseny/banshee,dufoli/banshee,mono-soc-2011/banshee,Dynalon/banshee-osx,mono-soc-2011/banshee,directhex/banshee-hacks,arfbtwn/banshee,petejohanson/banshee,stsundermann/banshee,Dynalon/banshee-osx,GNOME/banshee,arfbtwn/banshee,petejohanson/banshee,allquixotic/banshee-gst-sharp-work,GNOME/banshee,babycaseny/banshee,arfbtwn/banshee,ixfalia/banshee,dufoli/banshee,arfbtwn/banshee,mono-soc-2011/banshee,Dynalon/banshee-osx,Dynalon/banshee-osx,arfbtwn/banshee,petejohanson/banshee,stsundermann/banshee,stsundermann/banshee,GNOME/banshee,Dynalon/banshee-osx,Dynalon/banshee-osx,dufoli/banshee,babycaseny/banshee,Dynalon/banshee-osx,babycaseny/banshee,mono-soc-2011/banshee,Carbenium/banshee,dufoli/banshee,lamalex/Banshee,allquixotic/banshee-gst-sharp-work,stsundermann/banshee,dufoli/banshee,babycaseny/banshee,ixfalia/banshee,dufoli/banshee,arfbtwn/banshee,ixfalia/banshee,arfbtwn/banshee,directhex/banshee-hacks,ixfalia/banshee,dufoli/banshee,stsundermann/banshee,Carbenium/banshee,directhex/banshee-hacks,petejohanson/banshee,lamalex/Banshee,petejohanson/banshee,babycaseny/banshee,stsundermann/banshee,Carbenium/banshee,lamalex/Banshee,allquixotic/banshee-gst-sharp-work,Carbenium/banshee,mono-soc-2011/banshee,stsundermann/banshee,mono-soc-2011/banshee,Carbenium/banshee