Support uglified filter code

Hi.
As you probably know, [there are issues](https://github.com/mleibman/SlickGrid/issues/301) with minified code of filter function.

In this little patch you can find fixes for two cases I've met:
- [x] no semicolon/curly bracket at the end of filter body
- [x] do not drop curly brackets

Not sure if this patch can completely close #301, but it works for me.