D-Bus (old): Fix interface unregistration on error path

It is possible for this function to be called even if D-Bus interface
registration has failed. Avoid a D-Bus assert in such a case.

Signed-off-by: Jouni Malinen <j@w1.fi>

wpa_supplicant/dbus/dbus_old.c

@@ -712,7 +712,7 @@ int wpas_dbus_unregister_iface(struct wpa_supplicant *wpa_s)
 	if (wpa_s == NULL || wpa_s->global == NULL)
 		return 0;
 	ctrl_iface = wpa_s->global->dbus;
-	if (ctrl_iface == NULL)
+	if (ctrl_iface == NULL || wpa_s->dbus_path == NULL)
 		return 0;
 
 	con = ctrl_iface->con;