test,http: check that http server is robust from handler abuse

The only way I could find to complete coverage for _http_common.js is to
use semi-private (exposed but probably shouldn't be) handlers to get the
state into something weird. With the if-condition being checked (see
Refs) commented out, I get this result from this test:

```
node:_http_common:140
  if (len > 0 && !stream._dumped) {
                         ^

TypeError: Cannot read property '_dumped' of null
    at HTTPParser.parserOnBody (node:_http_common:140:26)
```

With the check in place, the test passes without an error. Seems like
quite the edge case, but I'm going to assume it's there for a reason.

Refs: https://coverage.nodejs.org/coverage-b560645d6b0a4bed/lib/_http_common.js.html#L137

PR-URL: #37958
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-http-req-close-robust-from-tampering.js

@@ -0,0 +1,26 @@
+'use strict';
+const common = require('../common');
+const { createServer } = require('http');
+const { connect } = require('net');
+
+// Make sure that calling the semi-private close() handlers manually doesn't
+// cause an error.
+
+const server = createServer(common.mustCall((req, res) => {
+  req.client._events.close.forEach((fn) => { fn.bind(req)(); });
+}));
+
+server.unref();
+
+server.listen(0, common.mustCall(() => {
+  const client = connect(server.address().port);
+
+  const req = [
+    'POST / HTTP/1.1',
+    'Content-Length: 11',
+    '',
+    'hello world',
+  ].join('\r\n');
+
+  client.end(req);
+}));