UX/PERF: Update readers count when a post from another user is read. Don't fetch the post data again just to update the count. (#8078)

app/models/post.rb

@@ -170,6 +170,11 @@ class Post < ActiveRecord::Base
     end
   end
 
+  def readers_count
+    read_count = reads - 1 # Excludes poster
+    read_count < 0 ? 0 : read_count
+  end
+
   def publish_change_to_clients!(type, opts = {})
     # special failsafe for posts missing topics consistency checks should fix,
     # but message is safe to skip