problem is that the offsets/sizes are of different type than ptrdiff_t,
and when using without casting, the resulting address is way off...

Change-Id: I7b1cdd611c8c4b317cd33ca8fbbda2e7e8f5f4fc
Reviewed-on: https://gerrit.libreoffice.org/16938Reviewed-by: David Ostrovsky <david@ostrovsky.org>
Tested-by: Jenkins <ci@libreoffice.org>
(cherry picked from commit 1b4d27a3)
Reviewed-on: https://gerrit.libreoffice.org/16950