LibreOffice doens't distinguish between sideWall and backWall.
It is controlled by the same Wall property.

Change-Id: If1919cf0a9bad3e80544cc5b2ae0f40f606febeb
Reviewed-on: https://gerrit.libreoffice.org/49429Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Bartosz Kosiorek <gang65@poczta.onet.pl>
(cherry picked from commit ff63bae0)
Reviewed-on: https://gerrit.libreoffice.org/50679Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>