#4312 Move handleMdiWindowClosed call from widget destructors to MdiSubWindow closeEvent

* This way the mdi window still exists at the time of removal and we can handle the removal orderly

ApplicationCode/UserInterface/RiuViewer.cpp

@@ -185,8 +185,6 @@ RiuViewer::~RiuViewer()
 {
     if (m_rimView)
     {
-        m_rimView->handleMdiWindowClosed();
-
         m_rimView->setCameraPosition(m_mainCamera->viewMatrix());
         m_rimView->setCameraPointOfInterest(pointOfInterest());
     }