dmap: Notify when there are no results
dmap: Notify when there are no results

This fixes https://bugzilla.gnome.org/show_bug.cgi?id=652516

vrutkovs/grilo-plugins,kyoushuu/grilo-plugins,GNOME/grilo-plugins,jasuarez/grilo-plugins,MikePetullo/grilo-plugins,vrutkovs/grilo-plugins,kyoushuu/grilo-plugins,grilofw/grilo-plugins,MathieuDuponchelle/grilo-plugins,MathieuDuponchelle/grilo-plugins,MathieuDuponchelle/grilo-plugins,MikePetullo/grilo-plugins,MathieuDuponchelle/grilo-plugins,grilofw/grilo-plugins,vrutkovs/grilo-plugins,jasuarez/grilo-plugins,MikePetullo/grilo-plugins,vrutkovs/grilo-plugins,kyoushuu/grilo-plugins,GNOME/grilo-plugins