Spurious Flush() in display.capture()

[ggcrunchy]

Basically, display.capture() and friends seem to be the only cases where the second overload of Scene::Render() is called. From what I can tell these never need the Flush(); I believe it's just a copy-paste artifact.

It's a no-op on most platforms.[1] On Windows, though, it calls SwapBuffers(). You can see this if you try the CaptureToFile code sample, where you get a black image for a frame; without the Flush() you don't. From my admittedly foggy recollection the other exceptions were similar "end of frame" / vsync logic.

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[1] - I'd have to review them to see where it isn't. I did the actual analysis almost a year ago, probably while investigating the Discord streaming crashes. I'm trying to distill a big diff into branches / PRs now, and had this on hand due to testing something or other with display.capture().