Fix group widgets appearing twice

dgl/src/NanoVG.cpp

@@ -932,6 +932,7 @@ NanoWidget::NanoWidget(NanoWidget* groupWidget)
       nData(new PrivateData(this))
 {
     pData->needsScaling = true;
+    pData->skipDisplay = true;
     groupWidget->nData->subWidgets.push_back(this);
 }
 

dgl/src/WidgetPrivateData.hpp

@@ -51,7 +51,10 @@ struct Widget::PrivateData {
           visible(true)
     {
         if (addToSubWidgets && groupWidget != nullptr)
+        {
+            skipDisplay = true;
             groupWidget->pData->subWidgets.push_back(self);
+        }
     }
 
     ~PrivateData()