FIX: Category description topics shouldn't auto-close

app/models/category.rb

@@ -151,6 +151,7 @@ SQL
   def create_category_definition
     t = Topic.new(title: I18n.t("category.topic_prefix", category: name), user: user, pinned_at: Time.now, category_id: id)
     t.skip_callbacks = true
+    t.auto_close_days = nil
     t.save!
     update_column(:topic_id, t.id)
     t.posts.create(raw: post_template, user: user)

app/models/topic.rb

@@ -605,7 +605,7 @@ class Topic < ActiveRecord::Base
   # TODO: change this method, along with category's auto_close_days. Use hours.
   def auto_close_days=(num_days)
     @ignore_category_auto_close = true
-    set_auto_close(num_days * 24)
+    set_auto_close( num_days ? num_days * 24 : nil)
   end
 
   def self.auto_close