Remove exception from skip_callback

[jeryRazakarison]

skip_callback will raise an exception if the callback is not set by Devise.
But Devise doesn't always set the callback send_on_create_confirmation_instructions, (for example when :confirmable is not present).
In several cases, with the master branch of Devise, we then have an error 500

Completed 500 Internal Server Error in 78ms (ActiveRecord: 0.0ms)
ArgumentError (After create callback :send_on_create_confirmation_instructions has not been defined):
...
/Users/jery/.rvm/gems/ruby-2.2.2/bundler/gems/devise_token_auth-d154b0294006/app/controllers/devise_token_auth/registrations_controller.rb:39:in `create'

Adding the option :raise to false (as stated in rails documentation), it doesn't raise an exception when the callback has not been set by Devise, and fixes issue #397

[britg]

@jeryRazakarison I'm running into this issue. Why did you close this PR? I can't find any further discussion on the correct way to do this.

[britg]

I ended up creating an override as below, but it seems an unnecessary hack?

class Overrides::RegistrationsController < DeviseTokenAuth::RegistrationsController

  def create
    resource_class.set_callback("create", :after, :send_on_create_confirmation_instructions)
    super
  end

end

[jeryRazakarison]

Hi @britg,
I closed this PR because it didn't pass the Travis Build, and so there was a risk it created unwanted side effects for other users.
I ended up overriding the create method following these instructions https://github.com/lynndylanhurley/devise_token_auth#custom-controller-overrides, but using
resource_class.skip_callback("create", :after, :send_on_create_confirmation_instructions, raise: false)
instead of
resource_class.skip_callback("create", :after, :send_on_create_confirmation_instructions)

I couldn't find a correction that passed the Travis CI build.

(Overriding was very efficient in my case, because I was able to make devise_token_auth works well with devise_invitable.)

[britg]

@jeryRazakarison Ok, thanks for the explanation. Looks like overriding is the way to go for now.