Make validations well-behaved with :deferred_encryption

[ghost]

Currently the following doesn't work:

  validates :name, presence: true
  encrypt_with_public_key :name,
    :symmetric => :never,
    :public_key => Rails.root.join('config','public.pem'),
    :deferred_encryption => true

As :deferred_encryption will initially result in the raw content being kept in the model instance and blank? and nil? were only well-defined for when it's kept encrypted.

[spikex]

Thank you!