Don't join on tags unnecessarily when matching all tags

lib/topic_query.rb

@@ -459,7 +459,6 @@ class TopicQuery
         result = result.preload(:tags)
 
         if @options[:tags] && @options[:tags].size > 0
-          result = result.joins(:tags)
 
           if @options[:match_all_tags]
             # ALL of the given tags:
@@ -476,6 +475,7 @@ class TopicQuery
             end
           else
             # ANY of the given tags:
+            result = result.joins(:tags)
             if @options[:tags][0].is_a?(Integer)
               result = result.where("tags.id in (?)", @options[:tags])
             else