FIX: robots.txt should be accessible even when login is required

app/controllers/robots_txt_controller.rb

@@ -1,14 +1,9 @@
 class RobotsTxtController < ApplicationController
   layout false
-  skip_before_filter :preload_json, :check_xhr
+  skip_before_filter :preload_json, :check_xhr, :redirect_to_login_if_required
 
   def index
-    path = if SiteSetting.allow_index_in_robots_txt
-      :index
-    else
-      :no_index
-    end
-
+    path = SiteSetting.allow_index_in_robots_txt ? :index : :no_index
     render path, content_type: 'text/plain'
   end
 end