write valid dxf record, related fdo#71971

Change-Id: I99f4dfca78cc0fd5d9b947000a99f8414c2a899b
(cherry picked from commit 7415fc31f5cdf7ff3f78dd304b9576b931a82aeb)
Reviewed-on: https://gerrit.libreoffice.org/6878
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>