QQuickWindow::sceneGraphInvalidated() signal is not always emitted

QQuickWindow::sceneGraphInvalidated() signal is not always emitted because if the render context is deleted after the window has been deleted then it is not going to be emitted. This is happening on Windows at least due to the fact that the render context is only deleted when the application does the final cleanup which is after the window itself has been deleted.

This is reproducible in the openglunderqml example which has a slot connected to sceneGraphInvalidated() and this is never called.