Full screen leaves white border around game window

[DukeSkinny]

When I toggle full screen mode, there's a very thin white strip enclosing the game window.

[fleroviux]

This was a conscious tradeoff due to borderless fullscreen windows causing the menu bar to not work correctly on Windows (see https://doc.qt.io/qt-5/windows-issues.html#fullscreen-opengl-based-windows). Needs evaluation if there is a different fix for the original issue that can be applied.