so the tooltip rectangle is wrong and doesn't shown under mutter

we could use pCtrl->OutputToScreenPixel(Point(0, 0)) here too

Change-Id: I75a717127ad75a4aac2cb9c22e526419f798ea99
Reviewed-on: https://gerrit.libreoffice.org/52654Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
(cherry picked from commit 7d95ef51)