FIX: ensure CategoryUser consistency

app/jobs/scheduled/ensure_db_consistency.rb

@@ -13,6 +13,7 @@ module Jobs
       UserStat.update_view_counts(13.hours.ago)
       Topic.ensure_consistency!
       Badge.ensure_consistency!
+      CategoryUser.ensure_consistency!
     end
   end
 end

app/models/category_user.rb

@@ -92,6 +92,10 @@ class CategoryUser < ActiveRecord::Base
     )
   end
 
+  def self.ensure_consistency!
+    exec_sql("DELETE FROM category_users WHERE user_id NOT IN (SELECT id FROM users)")
+  end
+
   private_class_method :apply_default_to_topic, :remove_default_from_topic
 end