OGL: Use a fixed VAO for attributeless rendering.

Instead of abusing whatever VAO is previously bound, which might have
enabled arrays.

Only used in one instance currently, which fixes a crash with older
NVIDIA drivers.

Source/Core/VideoBackends/OGL/Render.cpp

@@ -686,6 +686,8 @@ void Renderer::Shutdown()
 
 	delete m_post_processor;
 	m_post_processor = nullptr;
+
+	OpenGL_DeleteAttributelessVAO();
 }
 
 void Renderer::Init()