Do not emit proxyRes event when server is false. Work around http-party#548

Author: cheddar

lib/http-proxy/passes/web-incoming.js

@@ -117,7 +117,9 @@ web_o = Object.keys(web_o).map(function(pass) {
     (options.buffer || req).pipe(proxyReq);
 
     proxyReq.on('response', function(proxyRes) {
-      server.emit('proxyRes', proxyRes);
+      if (server) { // Workaround for https://github.com/nodejitsu/node-http-proxy/issues/548
+        server.emit('proxyRes', proxyRes);
+      }
       for(var i=0; i < web_o.length; i++) {
        if(web_o[i](req, res, proxyRes)) { break; }
       }