Don't unref cancelled SoupMessage
Don't unref cancelled SoupMessage

The SoupMessage that is cancelled in the dispose handler doesn't
belong us, it has already been queued. This fixes a crash that
occured when a GUPnPService object is disposed before the initial
introspection call has finished.

GNOME/gupnp,GNOME/gupnp,GNOME/gupnp,GNOME/gupnp