optical-media: Handle cancelled retvals like errors
optical-media: Handle cancelled retvals like errors

https://bugzilla.gnome.org/show_bug.cgi?id=722629

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