Avoid WebLogic NullPointerException with requests that contain "../".

If you send the following request to a WebLogic server using this combo service:

>combo?../a.js 

You will get a NullPointerException because ServletContext.getRealPath() is going to produce null and print out a stack trace to the browser.

I added a null check to avoid this, but combo service with "../" in the requests are still not going to load actual javascript or css resources in WebLogic.