EMF+: Integer coordinate values are signed.

Previously any coordinates with negative values would not be rendered
(as they would incorrectly appear to be outside the visible area).

(cherry picked from commit d8dedc775cedf0e9daf9284bc7e3a0331ccd2963)

Change-Id: I5babcec50d48dc2a6288a01685db61fbb7058680
Reviewed-on: https://gerrit.libreoffice.org/7247
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>