Check `params` is defined

`params` is not defined in some case, for example when using ActionMailer.

```
class UserMailer < ActionMailer::Base
  def send_email_without_args
    mail(
      to:      'to@example.com',
      from:    'from@example.com',
      subject: 'Action Args!!!',
      body:    'test'
    )
  end
end

UserMailer.send_email_without_args
#=> NameError: undefined local variable or method `params' for #<UserMailer:0x007f7f50f124b8>
       from /Users/fukayatsu/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/bundler/gems/action_args-b5a9d108778a/lib/action_args/abstract_controller.rb:8:in `send_action'
```