clearly we do not often have combobox's that have nothing selected,
otherwise these issues would have arisen sooner.
The immediate cause of fixing this was the assert
VCLXListBox::getSelectedItemPos which was triggered when using X-ray to
examine a writer document
Change-Id: Ia5ec713ef54a841010a9b680d4520f7160d48167
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/177532
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
b938c891e1