[Bug 45724] Multiple EndScene calls result in multiple glFlush (FF XIV)

https://bugs.winehq.org/show_bug.cgi?id=45724

--- Comment #4 from Andrew Wesie  ---
(In reply to Henri Verbeet from comment #3)
> I don't think we need a formal unit test for this, although that would be
> ideal. Some manual testing may be enough, but note that this would affect
> d3d8 and ddraw as well.

Looking at the wine ddraw module, I am wondering if maybe we need the flush in
EndScene iff there are no back buffers. If there is a back buffer, then the
client should need to call present, which will call wglSwapBuffers and do an
implicit flush. Otherwise, we are drawing directly to the front buffer and need
to flush in EndScene.