Resolves: fdo#86662 don't crash on docx load

ok in master, so just don't crash in 4-3 series

Change-Id: I2dcb7b0434341ff8058bdbdfc065ad08bd0600bc
Reviewed-on: https://gerrit.libreoffice.org/13374
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>
(cherry picked from commit dcc914ab55feb844d5d71e6568801fa1ffd47f6c)
Reviewed-on: https://gerrit.libreoffice.org/13375
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>
Tested-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>