message: Clear error code.
diff: @@ -3822,6 +3822,9 @@ static int swoole_mysql_coro_onWrite(swReactor *reactor, swEvent *event)
  SwooleG.main_reactor->set(SwooleG.main_reactor, event->fd, PHP_SWOOLE_FD_MYSQL_CORO | SW_EVENT_READ);
  //connected
  event->socket->active = 1;
  + client->connector.error_code = 0;
  + client->connector.error_msg = (char *) "";
  + client->connector.error_length = 0;
  client->handshake = SW_MYSQL_HANDSHAKE_WAIT_REQUEST;
  }
  else
  @@ -3849,7 +3852,8 @@ static int swoole_mysql_coro_onHandShake(mysql_client *client)
  swSysError("Read from socket[%d] failed.", cli->socket->fd);
  return SW_ERR;
  case SW_CLOSE:
  - _system_call_error: connector->error_code = errno;
  + _system_call_error:
  + connector->error_code = errno;
  connector->error_msg = strerror(errno);
  connector->error_length = strlen(connector->error_msg);
  swoole_mysql_coro_onConnect(client);
  