thumbnailer: Update skeleton to fix a possible crash
thumbnailer: Update skeleton to fix a possible crash

If the loader returns a NULL pixbuf without returning an
error, the skeleton would crash trying to print the error.
Print that the thumbnailer is broken instead.

https://bugzilla.gnome.org/show_bug.cgi?id=778204

GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf