stream_dvb: add missing mutex unlock

This deadlock was not triggered in real use since configuration
validity does not change at runtime.

closes #9459

stream/stream_dvb.c

@@ -1045,6 +1045,7 @@ static int dvb_open(stream_t *stream)
     }
 
     if (!dvb_parse_path(stream)) {
+        pthread_mutex_unlock(&global_dvb_state_lock);
         goto err_out;
     }