This allows an unnecessary GDIMetaFile -> WMF -> GDIMetaFile roundtrip,
and also avoids the odd black border at the bottom / right of the
preview metafile in the PDF import-as-graphic filter.

Change-Id: I7e3e782bbe0cf56def352e23b60864bb7773b607
Reviewed-on: https://gerrit.libreoffice.org/26743Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>