[fix] do not use middleware code if it's not needed

lib/node-http-proxy.js

@@ -166,7 +166,7 @@ exports.createServer = function () {
  switch (typeof arg) {
  case 'string': host = arg; break;
  case 'number': port = arg; break;
- case 'function': middleware.push(arg); break;
+ case 'function': middleware.push(handler = callback = arg); break;
  case 'object': options = arg; break;
  };
  });
@@ -203,11 +203,15 @@ exports.createServer = function () {
  }
  }
 
- if (middleware.length) {
+ if (middleware.length /*> 1*/) {
  //handler = callback = middleware.shift()
  //else if (middleware.length)
  handler = callback = stack(middleware, proxy);
  }
+ else if (middleware.length) { //do not use middleware code if it's not needed.
+ var h = middleware[0]
+ handler = callback = function (req,res) { h(req,res,proxy) };
+ }
 
  if (!handler) {
  //