trivial: Fix a crash when subsuming an application with itself
trivial: Fix a crash when subsuming an application with itself

kalev/appstream-glib,hughsie/appstream-glib,ximion/appstream-glib,ximion/appstream-glib,superm1/appstream-glib,kalev/appstream-glib,ximion/appstream-glib,mitya57/appstream-glib,mitya57/appstream-glib,hughsie/appstream-glib,superm1/appstream-glib,hughsie/appstream-glib,ikeydoherty/appstream-glib,ikeydoherty/appstream-glib