Reads the latest client crash record for a single client.

def ReadClientCrashInfo(self, client_id, cursor=None):
    """Reads the latest client crash record for a single client."""
    cursor.execute(
        "SELECT UNIX_TIMESTAMP(timestamp), crash_info "
        "FROM clients, client_crash_history WHERE "
        "clients.client_id = client_crash_history.client_id AND "
        "clients.last_crash_timestamp = client_crash_history.timestamp AND "
        "clients.client_id = %s", [db_utils.ClientIDToInt(client_id)])
    row = cursor.fetchone()
    if not row:
      return None

    timestamp, crash_info = row
    res = rdf_client.ClientCrash.FromSerializedString(crash_info)
    res.timestamp = mysql_utils.TimestampToRDFDatetime(timestamp)
    return res