GetODFSaneDefaultVersion() is surprisingly hot, mostly because it is
called from every ScXMLExport::WriteCell call, so cache it
Change-Id: Ibc54c007f4979315487badc23889eb264b11d4ca
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/174671
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
