because if the opengl support is such that the opengl-for-vcl requirements don't
fit, then on the second run after discovering this (the first having restarted)
if you try opengl slide transitions libreoffice will just exit because it
thinks this first check of opengl-for-slideshow is the first opengl-for-vcl effort.

so move this code into the place which I believe is the opengl-for-vcl entry point

this is all related to...

commit 210c39dd
Date:   Fri Jun 3 09:25:13 2016 +0300

    tdf#100193: Check earlier and harder whether OpenGL is good enough on Windows

Change-Id: I3f6a72efff9c533ca9a0602227fd929ac645f60b
Reviewed-on: https://gerrit.libreoffice.org/31763Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>