The userformscontainers is required property to pass checks in
getter/setter, but returning true instead of actual type is
not a best idea. So let's return actually expected dummy empty
container.

Change-Id: I5cc3e5462ed82f6f2f8e5a45d9fc2d9f9ce1c76f
Reviewed-on: https://gerrit.libreoffice.org/67431
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
(cherry picked from commit 24e7d982)
Reviewed-on: https://gerrit.libreoffice.org/70234Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>