BUG #16744: Resources are not removed for a renderer removed from the…

… window.

A loop where the render window is kept around and everything in the pipeline is removed
and added at the next iteration leaks memory, in OpenGL, linux. For the OpenGL2 backend same
loop does not leak.

Rendering/Core/vtkRenderWindow.cxx

@@ -828,6 +828,7 @@ void vtkRenderWindow::RemoveRenderer(vtkRenderer *ren)
   // we are its parent
   if (ren->GetRenderWindow() == this)
     {
+    ren->ReleaseGraphicsResources(this);
     ren->SetRenderWindow(NULL);
     }
   this->Renderers->RemoveItem(ren);