fix TreeWalker scan order (#3114)

fixes #3113

lib/ast.js

@@ -543,12 +543,11 @@ var AST_Call = DEFNODE("Call", "expression args", {
         args: "[AST_Node*] array of arguments"
     },
     _walk: function(visitor) {
-        return visitor._visit(this, function(){
-            var args = this.args;
-            for (var i = 0, len = args.length; i < len; i++) {
-                args[i]._walk(visitor);
-            }
+        return visitor._visit(this, function() {
             this.expression._walk(visitor);
+            this.args.forEach(function(node) {
+                node._walk(visitor);
+            });
         });
     }
 });