Fix #2990: Wiki Autocomplete Misses On Certain Meta-wikis

/wiki_pages?search[order]=post_count didn't include wiki pages that
didn't belong to a tag. This was due to doing an inner join on the tags
table instead of a left outer join.

app/models/artist.rb

@@ -437,7 +437,7 @@ class Artist < ActiveRecord::Base
       when "updated_at"
         q = q.order("artists.updated_at desc")
       when "post_count"
-        q = q.joins(:tag).order("tags.post_count desc")
+        q = q.includes(:tag).order("tags.post_count desc nulls last").references(:tags)
       else
         q = q.order("artists.id desc")
       end

app/models/wiki_page.rb

@@ -87,7 +87,7 @@ class WikiPage < ActiveRecord::Base
       when "title"
         q = q.order("title")
       when "post_count"
-        q = q.joins(:tag).order("tags.post_count desc")
+        q = q.includes(:tag).order("tags.post_count desc nulls last").references(:tags)
       else
         q = q.order("updated_at desc")
       end

test/functional/wiki_pages_controller_test.rb

@@ -28,6 +28,11 @@ class WikiPagesControllerTest < ActionController::TestCase
         get :index, {:search => {:title => "abc"}}
         assert_redirected_to(wiki_page_path(@wiki_page_abc))
       end
+
+      should "list wiki_pages without tags with order=post_count" do
+        get :index, {:search => {:title => "abc", :order => "post_count"}}
+        assert_redirected_to(wiki_page_path(@wiki_page_abc))
+      end
     end
 
     context "show action" do