message: fix swoole_async_readfile memory leak.
diff: @@ -264,7 +264,6 @@ static void php_swoole_aio_onComplete(swAio_event *event)
  #else
  zcontent = &_zcontent;
  #endif
  - memset(event->buf + ret, 0, 1);
  SW_ZVAL_STRINGL(zcontent, event->buf, ret, 1);
  }
  else if (event->type == SW_AIO_WRITE)
  @@ -810,6 +809,7 @@ PHP_FUNCTION(swoole_async_set)
  }
  }
  #endif
  + sw_zval_ptr_dtor(&zset);
  }
  PHP_FUNCTION(swoole_async_dns_lookup)
  