fdo#77229 EMF+ rendering: improve EmfPlusSetClipPath's CombineModeExclude case

This is still not perfect, but at least we now don't do the opposite of
what was asked.

Change-Id: I5e144c5ec2987902e65b2eb472259d9c39bbbd11
(cherry picked from commit c2af50eb6df396c957890a6b912b8f3185893551)
Reviewed-on: https://gerrit.libreoffice.org/8904
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>