Check for the case an AST_For's init is an EmptyStatement

(lame fix for #503)

lib/output.js

@@ -656,7 +656,7 @@ function OutputStream(options) {
         output.print("for");
         output.space();
         output.with_parens(function(){
-            if (self.init) {
+            if (self.init && !(self.init instanceof AST_EmptyStatement)) {
                 if (self.init instanceof AST_Definitions) {
                     self.init.print(output);
                 } else {