http: fix undefined error in parser event

The current check for socket.server[kIncomingMessage] does not
account for the possibility of a socket.server that doesn't
have that property defined. Fix it.

PR-URL: nodejs#20029
Fixes: nodejs#19231
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Khaidi Chu <i@2333.moe>

lib/_http_common.js

@@ -62,7 +62,8 @@ function parserOnHeaders(headers, url) {
 function parserOnHeadersComplete(versionMajor, versionMinor, headers, method,
                                  url, statusCode, statusMessage, upgrade,
                                  shouldKeepAlive) {
-  var parser = this;
+  const parser = this;
+  const { socket } = parser;
 
   if (!headers) {
     headers = parser._headers;
@@ -75,10 +76,11 @@ function parserOnHeadersComplete(versionMajor, versionMinor, headers, method,
   }
 
   // Parser is also used by http client
-  var ParserIncomingMessage = parser.socket && parser.socket.server ?
-    parser.socket.server[kIncomingMessage] : IncomingMessage;
+  const ParserIncomingMessage = (socket && socket.server &&
+                                 socket.server[kIncomingMessage]) ||
+                                 IncomingMessage;
 
-  parser.incoming = new ParserIncomingMessage(parser.socket);
+  parser.incoming = new ParserIncomingMessage(socket);
   parser.incoming.httpVersionMajor = versionMajor;
   parser.incoming.httpVersionMinor = versionMinor;
   parser.incoming.httpVersion = `${versionMajor}.${versionMinor}`;