and give utl::OStreamWrapper a new constructor so that it knows it is
taking ownership of  the SvStream, which appears to fix several leaks

Change-Id: Idcbcca9b81a4f0345fd8b8c8a2f4e84213686a6b
Reviewed-on: https://gerrit.libreoffice.org/57187
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>