Report VNC tag only when valid.

def vncport(dom):

    """VNC port for the VM console access."""

    try:

        return et.ElementTree().parse(

        port = et.ElementTree().parse(

            StringIO(dom.lv_dom.XMLDesc(0))

        ).find('devices/graphics').get('port')

    except Exception:

        logger.exception('VNCPort')

        raise

    if 0 < port < 65536:

        return port

    return

@ttl(10)