Fix check RegExp if value.length == 0

If input not set to required, val == '' is valid. I think.

If input set required, regexp and val == '' then displayed only required message. This is correct.
![1](https://f.cloud.github.com/assets/3757319/869254/2c9feef0-f7f0-11e2-99bf-efd742ed0385.png)
![2](https://f.cloud.github.com/assets/3757319/869255/31b7930c-f7f0-11e2-8005-9c8b081abd29.png)