grab highest post number from the raw data, so deletions at the end of a topic work

lib/topic_view.rb

@@ -223,6 +223,15 @@ class TopicView
     @suggested_topics ||= TopicQuery.new(@user).list_suggested_for(topic)
   end
 
+  # This is pending a larger refactor, that allows custom orders
+  #  for now we need to look for the highest_post_number in the stream 
+  #  the cache on topics is not correct if there are deleted posts at 
+  #  the end of the stream (for mods), nor is it correct for filtered 
+  #  streams
+  def highest_post_number
+    @highest_post_number ||= @posts.maximum(:post_number)
+  end
+
   protected
 
   def read_posts_set