RTP / RTSP elements: fix event seqnums

gst/rtsp/gstrtspsrc.c

@@ -3222,6 +3222,9 @@ udpsrc_probe_cb (GstPad * pad, GstPadProbeInfo * info, gpointer user_data)
 
   switch (GST_EVENT_TYPE (info->data)) {
     case GST_EVENT_SEGMENT:
+      if (!gst_event_is_writable (info->data))
+        info->data = gst_event_make_writable (info->data);
+
       *segment_seqnum = gst_event_get_seqnum (info->data);
     default:
       break;