trivial: When parsing the extra AppStream file, use the filename in the error
trivial: When parsing the extra AppStream file, use the filename in the error

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