in the FastParser case, those name/prefix fields in context are not
initialised, so don't warn for that case
Change-Id: I485dd1b86d81ea2b6f03fa6a8ecf5fb23d46a8e1
Reviewed-on: https://gerrit.libreoffice.org/83153
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>