regression from
    commit 404630c6
    simplify Bitmap operator==/IsEqual (stage1)

Change-Id: Ifabbfb28e0ccbe28b19db7f2c50e6d6f55569f9a
Reviewed-on: https://gerrit.libreoffice.org/43239Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>