fix: pipe stream inside error handler

[climba03003]

Fix when pipe stream inside custom handler, it will cause an error because of undefined header being set.

This issue is found by poloniumcz in Discord Server.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[RafaelGSS]

LGTM.

[climba03003]

Alternative solution (It maybe a Breaking Change):

We change the removeHeader and update the value as undefined. Then, we delete the unwanted one at the very last stage.

...

Reply.prototype.removeHeader = function (key) {
  // Node.js does not like headers with keys set to undefined,
  // so we have to delete the key.
  this[kReplyHeaders][key.toLowerCase()] = undefined
  return this
}

...

function onSendEnd (reply, payload) {
  const res = reply.raw
  const req = reply.request
  const statusCode = res.statusCode

  // we clean up the header at the very last stage
  // it can minimize the number of times using `delete`
  const keys = Object.keys(reply[kReplyHeaders])
  /* eslint-disable no-var */
  for (var i = 0; i !== keys.length; ++i) {
    const key = keys[i]
    if (reply[kReplyHeaders][key] === undefined) delete reply[kReplyHeaders][key]
  }

  if (payload === undefined || payload === null) {
    reply[kReplySent] = true

    // according to https://tools.ietf.org/html/rfc7230#section-3.3.2
    // we cannot send a content-length for 304 and 204, and all status code
    // < 200.
    // For HEAD we don't overwrite the `content-length`
    if (statusCode >= 200 && statusCode !== 204 && statusCode !== 304 && req.method !== 'HEAD') {
      reply[kReplyHeaders]['content-length'] = '0'
    }

    res.writeHead(statusCode, reply[kReplyHeaders])
    // avoid ArgumentsAdaptorTrampoline from V8
    res.end(null, null, null)
    return
  }

  if (typeof payload.pipe === 'function') {
    reply[kReplySent] = true

    sendStream(payload, res, reply)
    return
  }

  if (typeof payload !== 'string' && !Buffer.isBuffer(payload)) {
    throw new FST_ERR_REP_INVALID_PAYLOAD_TYPE(typeof payload)
  }

  if (!reply[kReplyHeaders]['content-length']) {
    reply[kReplyHeaders]['content-length'] = '' + Buffer.byteLength(payload)
  } else if (req.raw.method !== 'HEAD' && reply[kReplyHeaders]['content-length'] !== Buffer.byteLength(payload)) {
    reply[kReplyHeaders]['content-length'] = '' + Buffer.byteLength(payload)
  }

  reply[kReplySent] = true

  res.writeHead(statusCode, reply[kReplyHeaders])

  // avoid ArgumentsAdaptorTrampoline from V8
  res.end(payload, null, null)
}

[mcollina]

lgtm

[mcollina]

I find this solution correct

[github-actions]

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