Resolves: rhbz#1089377 crash on loading a specific rtf

(cherry picked from commit 5aeaba2e6592dab0404301dcef644144f82ffcbf)

Change-Id: I26864f3a2247f5d7184f395cfed91eaf92e36295
Reviewed-on: https://gerrit.libreoffice.org/9131
Tested-by: David Tardon <dtardon@redhat.com>
Reviewed-by: David Tardon <dtardon@redhat.com>