message: To the safe side.
diff: @@ -1986,7 +1986,12 @@ int mysql_response(mysql_client *client)
  return SW_ERR;
  }
  buffer->offset += (4 + ret);
  +
  + // easy to the safe side: but under what circumstances would num_column will be 0 in result set?
  + if (client->response.num_column > 0)
  + {
  client->response.columns = ecalloc(client->response.num_column, sizeof(mysql_field));
  + }
  client->state = SW_MYSQL_STATE_READ_FIELD;
  break;
  }
  