MainFrame: cosmetics

[](){} confuses astyle sometimes.
[]{} does not.
MainFrame: adjust auto-zoom logic

When video size changes during playback, reposition the window only
if "auto-zoom" AND "limit window proportions" options are enabled.

Refs #3704
MainFrame: fix aero-snap misdetection

Fixes #4284
MainFrame: don't reset position when aero-snapped
MainFrame: don't access class as memory chunk
MainFrame: adjust auto-zoom logic yet more

We auto-zoom when we loose the video during playback.
So it makes sense to auto-zoom when we regain it too.
StatusBar: flickerless paint