Avoid creating our own OpenGLContext to render until we need to
refresh the screen.

Change-Id: I29d4a1cb6193c92ed77ae98566f8b897a6bc67b5
Reviewed-on: https://gerrit.libreoffice.org/20709Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>