Regression from commit d464d505
(Refactor calc non-linear ViewToDevice transform, 2018-10-12), the
problem was that the opengl menu was never painted from the starved idle
handler as a paint-invalidation loop starved the main loop.

ScGridWindow::Paint() called vcl::Window::ImplPosSizeWindow() for the
form control of the bugdoc, which triggered an invalidation -> paint ->
start again.

Checking what adjustControlGeometry_throw() did, the result of the
transformed points are quite close to each other, but not equivalent:

debug:18521:18521: adjustControlGeometry_throw: aTopLeft before transformation is (1773,426)
debug:18521:18521: adjustControlGeometry_throw: aTopLeft after transformation is (64.935,16.0382)
debug:18521:18521: adjustControlGeometry_throw: aPaintRectPixel is 952x586@(64,16)

If we round, rather than truncate, then the size of the control is
always the same, so no actual resize and invalidation happens during
paint.

Change-Id: Id55fd227e3ae7fc57d5253bc28f42b9b4315450e
Reviewed-on: https://gerrit.libreoffice.org/69821Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins