This patch fixes an issue that causes Qt3D's Viewport to be blank
when its renderMode property is set to BufferedRender.
(QSGPainterNode's RenderTarget is set to FramebufferObject)
Task-number: QTBUG-23862
Change-Id: Ic7a333f79ecf1aa153ef42e213644a17243a3580
Reviewed-by: Sarah Jane Smith <sarah.j.smith@nokia.com>
Reviewed-by: Yoann Lopes <yoann.lopes@nokia.com>