message: Fix bug: MySQL double free when io error occurred
diff: @@ -122,6 +122,8 @@ public:
  {
  non_sql_error(MYSQLND_CR_SERVER_GONE_ERROR, MYSQLND_SERVER_GONE " due to %s", socket->errMsg);
  }
  + /* don't send QUIT after IO error */
  + state = SW_MYSQL_STATE_CLOSED;
  close();
  }
  @@ -247,7 +249,7 @@ public:
  inline bool is_writable()
  {
  - return is_connect() && !socket->has_bound(SW_EVENT_WRITE);
  + return state != SW_MYSQL_STATE_CLOSED && is_connect() && !socket->has_bound(SW_EVENT_WRITE);
  }
  bool is_available_for_new_reuqest()
  