mss: Dump pipeline on errors

I had to debug a not link issue while reworking the pipeline.

src/main.c

@@ -32,12 +32,15 @@ sigint_handler (gpointer user_data)
 static gboolean
 gst_bus_cb (GstBus * bus, GstMessage * message, gpointer data)
 {
+  GstBin *pipeline = GST_BIN (data);
+
   switch (GST_MESSAGE_TYPE(message)) {
   case GST_MESSAGE_ERROR:
     {
       GError *gerr;
       gchar *debug_msg;
       gst_message_parse_error (message, &gerr, &debug_msg);
+      GST_DEBUG_BIN_TO_DOT_FILE (pipeline, GST_DEBUG_GRAPH_SHOW_ALL, "mss-pipeline-ERROR");
       g_error ("Error: %s (%s)", gerr->message, debug_msg);
       g_error_free (gerr);
       g_free (debug_msg);
@@ -160,7 +163,6 @@ webrtc_client_connected_cb (MssHttpServer *server, MssClientId client_id,
 
   gst_caps_unref (caps);
 
-
   g_signal_emit_by_name (webrtcbin, "create-offer", NULL,
       gst_promise_new_with_change_func (
           (GstPromiseChangeFunc) on_offer_created, webrtcbin,NULL));
@@ -258,18 +260,19 @@ static gboolean
 restart_source (gpointer user_data)
 {
   struct RestartData *rd = user_data;
-  GstElement *tsparse;
+  GstElement *e;
   GstStateChangeReturn ret;
 
   gst_element_set_state (rd->src, GST_STATE_NULL);
   gst_element_set_locked_state (rd->src, TRUE);
-  tsparse = gst_bin_get_by_name (GST_BIN (rd->pipeline), "tsparse");
+  e = gst_bin_get_by_name (GST_BIN (rd->pipeline), "srtqueue");
   gst_bin_add (GST_BIN (rd->pipeline), rd->src);
-  gst_element_link (rd->src, tsparse);
+  if (!gst_element_link (rd->src, e))
+    g_assert_not_reached ();
   gst_element_set_locked_state (rd->src, FALSE);
   ret = gst_element_set_state (rd->src, GST_STATE_PLAYING);
   g_assert (ret != GST_STATE_CHANGE_FAILURE);
-  gst_object_unref (tsparse);
+  gst_object_unref (e);
 
   g_debug ("Restarted source after EOS");
 
@@ -360,7 +363,7 @@ int main (int argc, char *argv[])
   g_free (pipeline_str);
 
   bus = gst_element_get_bus (pipeline);
-  gst_bus_add_watch (bus, gst_bus_cb, NULL);
+  gst_bus_add_watch (bus, gst_bus_cb, pipeline);
   gst_object_unref (bus);
 
   g_signal_connect (http_server, "ws-client-disconnected",