Dont do validate when validator="[]"

When using `validator="[]"` will cause this error https://github.com/kelp404/angular-validator/issues/9

![screen shot 2014-05-22 at 5 32 31 pm](https://cloud.githubusercontent.com/assets/2560096/3052000/202b7a34-e194-11e3-932f-4a5289ea4c94.png)