fdo#74823 RTF import: work around wrong table column width on invalid input

This scenario is not a valid one, Word doesn't handle it, either -- but
the old LO 3.4 parser did. So add minimal support for it to avoid
the regression.

(cherry picked from commit 0a215b9a980e68f899ad548f780bbe5a1fec8732)

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

Change-Id: Icc2e8d3bf314e9cadda57956668033aa6d092457
Reviewed-on: https://gerrit.libreoffice.org/8871
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>