We need to export date format and also text content
in case of empty date field. Otherwise the exported
date field will be lost during import into LO Writer
or MSO Word.

Reviewed-on: https://gerrit.libreoffice.org/66194
Tested-by: Jenkins
Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>
(cherry picked from commit 24613d7a)

Change-Id: I5cf65bedba010f64ca8f56262057f3cce32b0943
Reviewed-on: https://gerrit.libreoffice.org/66289Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>