FIX: Permalinks should redirect to category URL including the ID

This is a temporary fix. Urls for third-level categories should function without the id. Once that is fixed, this change can be reverted

app/models/permalink.rb

@@ -79,7 +79,7 @@ class Permalink < ActiveRecord::Base
     return external_url if external_url
     return "#{Discourse::base_uri}#{post.url}" if post
     return topic.relative_url if topic
-    return category.url if category
+    return "#{category.url}/#{category.id}" if category
     nil
   end
 

spec/models/permalink_spec.rb

@@ -62,7 +62,7 @@ describe Permalink do
 
     it "returns a category url when category_id is set" do
       permalink.category_id = category.id
-      expect(target_url).to eq(category.url)
+      expect(target_url).to eq("#{category.url}/#{category.id}")
     end
 
     it "returns nil when category_id is set but category is not found" do