preparatory to making the id part into strong_int

Change-Id: Ied96193a6db9d45b24267b51b3014eb923319598
Reviewed-on: https://gerrit.libreoffice.org/37027Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>