writable.writableEnded
在调用 writable.end() 之后是 true。此属性不指示数据是否已刷新，为此则使用 writable.writableFinished 代替。
¥Is true after writable.end() has been called. This property
does not indicate whether the data has been flushed, for this use
writable.writableFinished instead.