fdo#74499: - FILESAVE:System throws a segmentation fault while saving files

Description: Docx containing text frame giving segmentation fault while saving file.
Reason found is inside writeDMLTextFrame() it was getting SdrObject pointer which is NULL
and accessing this NULL pointer was giving seg fault.
issue is fixed with commit 4de30fa7fd6abb5c2ea2b63a0e306954f7acc1b1 here is the export test.

Conflicts:
	sw/qa/extras/ooxmlexport/ooxmlexport.cxx

Change-Id: I0ab4bbf2126abbfa0fa37d2156aa3390ded0997c
Reviewed-on: https://gerrit.libreoffice.org/7894
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>