Fix crash in warden hook

It seems that in some cases `action_dispatch.cookies` is not
set in the environment during the `after_authentication`
hook.

lib/two_factor_authentication/hooks/two_factor_authenticatable.rb

@@ -1,11 +1,9 @@
 Warden::Manager.after_authentication do |user, auth, options|
   reset_otp_state_for(user)
 
+  if auth.env["action_dispatch.cookies"]
     expected_cookie_value = "#{user.class}-#{user.id}"
     actual_cookie_value = auth.env["action_dispatch.cookies"].signed[TwoFactorAuthentication::REMEMBER_TFA_COOKIE_NAME]
-  if actual_cookie_value.nil?
-    bypass_by_cookie = false
-  else
     bypass_by_cookie = actual_cookie_value == expected_cookie_value
   end