NullStream write after end fix

[adipirro]

Since the stream needs to be reused, make it bypass the normal end process and just keep on eating put requests.

[coveralls]

Coverage decreased (-0.006%) to 90.547% when pulling df1b302 on adipirro:patch-1 into c65140c on Unity-Technologies:master.

[stephen-palmer]

hmm .. think I would feel better about just changing _onPut() to create a new NullStream each time.

In fact we could just simplify it further and do this inline:

this._putStream = new Writable({
  write(chunk, encoding, cb) {
    setImmediate(cb);
  }
});

Remove the NullStream class and _nullStream member var.

[adipirro]

That should work if you'd prefer it. It is how I initially tested the fix.

Since the null stream never changes however...I felt this way was a little nicer. All we need is a black hole to dump things in, no need to constantly allocate new null streams every time a put request is blacklisted.

[stephen-palmer]

I understand, i just think it's an over-optimization in this case. The normal mode of behavior would be to create a new stream for every PUT. This follow up PR is presumably required because there were side effects to the original cached null stream, which I think the proposed change will fix - but streams are sufficiently opaque/complex that I can't say for sure we're not missing anything.

Better to avoid the possibility all together by using new streams for each request, and it reduces overall complexity.

[stephen-palmer]

Thanks, looks good.