trivial: Do not print a critical warning when saving a pixbug that's not set
trivial: Do not print a critical warning when saving a pixbug that's not set

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