which lets us avoid constructing the decomposition when we are only
interesting in the bounding box, e.g. for hit testing

Change-Id: Icd8d430b75d207063f1db70e5a0822d5d82a7d00
Reviewed-on: https://gerrit.libreoffice.org/30835Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>