regression from...

commit 18d63606
Author: Caolán McNamara <caolanm@redhat.com>
Date:   Mon Jun 19 09:46:31 2017 +0100

    ofz: use OString instead of bare char*

this is no use to the reporter though, as the document format is
10 and 11 is the oldest the filter will open

Change-Id: I4cdfe92e37f047493a6eab95f0e8e9f5dced1a35
Reviewed-on: https://gerrit.libreoffice.org/68745
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>