Re-arrange the calling convention to make it obvious that
a valid stream is the same as a good (true) result.
Change-Id: I974b023a8e7231e70ab649628fdbe43c33001e5b
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/165874
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>