Refactor for lazy

I think it partially solves the issue. This is a scenario I have in mind (I didn't test it btw, but we do have something similar in our system):

```ruby
class Service < ActiveRecord::Model
  include CryptKeeper
  crypt_keeper_fields :password
  
  before_save do
    errors.add :base, :failure unless something
  end
  
end
```

Imagine we have a form that allows to set that password. When saving, crypt keeper will encrypt the password, and our model will run its before_save. If that before_save fails, the form will be shown again. At this point, wouldn't it display the actual encrypted value for password, as crypt keeper already run its `before_save :encrypt_fields`?