Fix #3231. Don't try to emit error on a null'ed req object

lib/http.js

@@ -1158,18 +1158,21 @@ ClientRequest.prototype.onSocket = function(socket) {
     // Setup "drain" propogation.
     httpSocketSetup(socket);
 
-    var errorListener = function(err) {
+    function errorListener(err) {
       debug('HTTP SOCKET ERROR: ' + err.message + '\n' + err.stack);
+      if (req) {
         req.emit('error', err);
         // For Safety. Some additional errors might fire later on
         // and we need to make sure we don't double-fire the error event.
         req._hadError = true;
+      }
       if (parser) {
         parser.finish();
         freeParser(parser, req);
       }
       socket.destroy();
     }
+
     socket.on('error', errorListener);
 
     socket.ondata = function(d, start, end) {