FIX: categories created by users who are deleted cannot be deleted

spec/components/user_destroyer_spec.rb

@@ -238,6 +238,17 @@ describe UserDestroyer do
         UserDestroyer.new(@admin).destroy(@user, {block_ip: true})
       end
     end
+
+    context 'user created a category' do
+      let!(:category) { Fabricate(:category, user: @user) }
+
+      it "assigns the system user to the categories" do
+        UserDestroyer.new(@admin).destroy(@user, {delete_posts: true})
+        category.reload.user_id.should == Discourse.system_user.id
+        category.topic.should be_present
+        category.topic.user_id.should == Discourse.system_user.id
+      end
+    end
   end
 
 end