fdo#75968 Fix OUString conversion

Change-Id: Ie865b16c163d47de34ab2fe23bb7432b7710877f
Reviewed-on: https://gerrit.libreoffice.org/8510
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>