Ensure default settings are exposed in UI

Without this change, `authorized_keys_enabled` is unchecked when it is nil, even if it should be checked by default.

app/controllers/admin/application_settings_controller.rb

@@ -53,7 +53,7 @@ class Admin::ApplicationSettingsController < Admin::ApplicationController
   private
 
   def set_application_setting
-    @application_setting = ApplicationSetting.current
+    @application_setting = current_application_settings
   end
 
   def application_setting_params