We need to distunguish when we have list format string, but it
is empty (no level text will be diplayed) or it does not exist
at all, so we need to fallback to old prefix-suffix syntax.
Change-Id: Ifd4ccd5a676db86c39d2ef48e91d191d92b9b2a0
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/94322
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>