timebasedwidget: don't update the viewer if it's the same

Minor optimization, since changing the viewer can be a complex process it should
only be done if absolutely necessary.

app/widget/timebased/timebased.cpp

@@ -48,6 +48,10 @@ ViewerOutput *TimeBasedWidget::GetConnectedNode() const
 
 void TimeBasedWidget::ConnectViewerNode(ViewerOutput *node)
 {
+  if (viewer_node_ == node) {
+    return;
+  }
+
   if (viewer_node_) {
     DisconnectNodeInternal(viewer_node_);