In case the input document used a PDF 1.5 xref stream, not an old xref
table, then write that as part of the incremental update. Acrobat seems
to require this.

Change-Id: I9f1f73140c26308f8720aa1ffe1b905d0e60ede0
Reviewed-on: https://gerrit.libreoffice.org/30724Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>