I remember that, before LibreOffice 4, "MZ23" used to be a magic
string which we could not see in the preview window as if there was
no node.

Change-Id: If80b77e1e24a2c5f8b3528fac8e9209b8c0b5954
Reviewed-on: https://gerrit.libreoffice.org/15893Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>