so that one meaningfully compare it; default is DataType::OTHER,
which is not comparable

Change-Id: Ifc1e1c9b801f45d0a95a83d30cc205b91e647880
Reviewed-on: https://gerrit.libreoffice.org/39212Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>