Fixed non existing unit with key "firstObject".

When I use jPanelMenu the following exception occurs.

![undefined unit](https://f.cloud.github.com/assets/504049/1939162/66334632-7f5c-11e3-9a94-4114a014073b.PNG)

Unfortunately I can't narrow this issue down. My best guess that it has something todo with Ember.js (a library that I use).

If we debug the exception you will see that there is another element in the array with the key "firstObject".

![undefined_firstobject](https://f.cloud.github.com/assets/504049/1939173/c09c0b18-7f5c-11e3-8ddc-649fdf646d69.png)

Fixing this is easy. Just switch to the normal for loop.