tsdemux: Don't set invalid seqnum on segment event

https://bugzilla.gnome.org/show_bug.cgi?id=796623
diff --git a/gst/mpegtsdemux/tsdemux.c b/gst/mpegtsdemux/tsdemux.c
index 35c7f29..e5c78e7 100644
--- a/gst/mpegtsdemux/tsdemux.c
+++ b/gst/mpegtsdemux/tsdemux.c
@@ -2476,7 +2476,9 @@
 
   if (!demux->segment_event) {
     demux->segment_event = gst_event_new_segment (&demux->segment);
-    gst_event_set_seqnum (demux->segment_event, base->last_seek_seqnum);
+
+    if (base->last_seek_seqnum != GST_SEQNUM_INVALID)
+      gst_event_set_seqnum (demux->segment_event, base->last_seek_seqnum);
   }
 
 push_new_segment: