0xFFFF cast to short turned into -1 so wasn't seen as > 8000

Change-Id: I57592020c3c31751bec43f2619bf65d41ac47e87
Reviewed-on: https://gerrit.libreoffice.org/65540
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>