Uploading a large file using stream.pipe(req) does not work

Uploading files larger than the read stream's highWatermark does not work.

This is tested with node 16.13.1

Sample server:
```
const express = require('express'),
fs = require('fs'),
http = require('http');

function upload(req, res) {
const out = fs.createWriteStream('/tmp/out');
req.pipe(out).on('finish', function () {
console.log('upload finished');
res.status(200).send({});
});
}

const app = express();
app.post('/upload', upload);

http.createServer({}, app).listen(3000, function () {
console.log('listening on port 3000');
});
```

You can test the server itself works using `curl -F file=@largefile.txt -X POST http://localhost:3000/upload`

Superagent upload code:
```
'use strict';

const fs = require('fs'),
superagent = require('superagent');

const readStream = fs.createReadStream('./largefile.txt');
const request = superagent.post('http://localhost:3000/upload')
request.on('response', function (response) {
console.log('got response', response.status);
});
readStream.pipe(request);
```

The code above will just "hang" if largefile.txt is more than twice the highWaterMark. For fs, the default water mark is 64KB. So, if the file is say 200KB, the upload code will hang.