FIX: never attempt to log invalid post numbers

Previously in some cases we would queue logging of invalid post numbers

The impact would be we would miss logging an incoming link and would leak
an error.

lib/topic_view.rb

@@ -481,6 +481,14 @@ class TopicView
     @filtered_posts.order(sort_order: :desc).limit(1).pluck(:id).first
   end
 
+  def current_post_number
+    if highest_post_number.present?
+      post_number > highest_post_number ? highest_post_number : post_number
+    else
+      nil
+    end
+  end
+
   protected
 
   def read_posts_set