hw/remote: guard listener unregister in finalize

Guard the unregister by checking whether the listener callback was
set, which only happens right before registration.

Cc: jag.raman@oracle.com
Fixes: c7d80c7c1d ("multi-process: Associate fd of a PCIDevice with its object")
Reviewed-by: Jagannathan Raman <jag.raman@oracle.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

hw/remote/remote-obj.c

@@ -154,7 +154,9 @@ static void remote_object_finalize(Object *obj)
     RemoteObjectClass *k = REMOTE_OBJECT_GET_CLASS(obj);
     RemoteObject *o = REMOTE_OBJECT(obj);
 
-    device_listener_unregister(&o->listener);
+    if (o->listener.unrealize) {
+        device_listener_unregister(&o->listener);
+    }
 
     if (o->ioc) {
         qio_channel_shutdown(o->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);