use rtl::Reference here since these are reference counted data
structures, and we hand out references to me via our API

Change-Id: I8f69dde2db08519cb3d9de20b4ad54462e3ecc98
Reviewed-on: https://gerrit.libreoffice.org/49180Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>