Problem:
- If the PPTX contains embedded table i.e copied from excel, when we open it in
impress it row height increase due to this table format changes.
- Table contents empty row i.e without text, then row height increase because
text height is added also added for empty row.

Solution:
- Added check whether row contents text or not.

Change-Id: I9f8a99aa407384505f0075168cf64fd51b8b4c7b
Reviewed-on: https://gerrit.libreoffice.org/14925Tested-by: Jenkins <ci@libreoffice.org>
Tested-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>