Fixes CVE-2017-1000158.

Change-Id: I1871f031e3431253a3403f2ea2b586bcc4aa1016
Reviewed-on: https://gerrit.libreoffice.org/56609
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
(cherry picked from commit 744feb55)
Reviewed-on: https://gerrit.libreoffice.org/56673Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
(cherry picked from commit f7642379)