Set default host on protocol==null

Some libraries set protocol to null instead of undefined, so we need to check for it here to allow default behaviour. Otherwise, we get the "Protocol not supported." error.

Author: tomaash

lib/XMLHttpRequest.js

@@ -284,6 +284,7 @@ exports.XMLHttpRequest = function() {
         break;
 
       case undefined:
+      case null:
       case "":
         host = "localhost";
         break;