http: null the joinDuplicateHeaders property on cleanup

Null the `joinDuplicateHeaders` property when the parser is freed.

Refs: https://github.com/nodejs/node/pull/45982
PR-URL: https://github.com/nodejs/node/pull/48608
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matthew Aitken <maitken033380023@gmail.com>

lib/_http_common.js

@@ -236,6 +236,7 @@ function cleanParser(parser) {
   parser[kOnTimeout] = null;
   parser._consumed = false;
   parser.onIncoming = null;
+  parser.joinDuplicateHeaders = null;
 }
 
 function prepareError(err, parser, rawPacket) {

test/parallel/test-http-parser-memory-retention.js

@@ -25,18 +25,24 @@ server.on('request', common.mustCall((request, response) => {
 }));
 
 server.listen(common.mustCall(() => {
-  const request = http.get({ port: server.address().port });
+  const request = http.get({
+    headers: { Connection: 'close' },
+    port: server.address().port,
+    joinDuplicateHeaders: true
+  });
   let parser;
 
   request.on('socket', common.mustCall(() => {
     parser = request.parser;
     assert.strictEqual(typeof parser.onIncoming, 'function');
+    assert.strictEqual(parser.joinDuplicateHeaders, true);
   }));
 
   request.on('response', common.mustCall((response) => {
     response.resume();
     response.on('end', common.mustCall(() => {
       assert.strictEqual(parser.onIncoming, null);
+      assert.strictEqual(parser.joinDuplicateHeaders, null);
     }));
   }));
 }));