another DrawingML export crash fix
another DrawingML export crash fix

Change-Id: I0386b4a768a9ac51cb86ac1c3edb17c41caf821a
Reviewed-on: https://gerrit.libreoffice.org/15993
Tested-by: Jenkins <5a4fe08359c7f97380e408c717ef42c86939cd86@libreoffice.org>
Reviewed-by: Andras Timar <a6d402970b646b92d0c38c744d46432a07992d80@collabora.com>

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core