fdo#70185: Correct and reenable SmNodeToTextVisitor's test case

This fixes the order of handling csub/csup changed at 80de3c0fe6b191f6d528ae1142737e2561b12ccd.

Change-Id: I1b5ad39b367e1933f8a17ce8126feed4d996f662
Reviewed-on: https://gerrit.libreoffice.org/13086
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>