Pointed out by lcov for the RTF import, but all of RTF/DOCX
import/export was missing.

DOC export is still missing.

Change-Id: I9c48a08c3e951409f59dc1631a6ab39aa95f905d
Reviewed-on: https://gerrit.libreoffice.org/67700
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>