Fix validator="[]" to pass validation

In last commit, when we use `validator="[]"`, angular-validator still going through the validation but error

I didn't get any success console 

![screen shot 2014-05-27 at 4 26 06 pm](https://cloud.githubusercontent.com/assets/2560096/3089117/e2af1518-e57a-11e3-95b8-7764e098ae6c.png)

I suppose that having `validator="[]"` input still need to do the validation procedure, so I add this.

Else, it can just ignore the procedure when having `validator="[]"`