Digest should exclude muted topics.

app/models/topic.rb

@@ -266,10 +266,12 @@ class Topic < ActiveRecord::Base
     topics = Topic
               .visible
               .secured(Guardian.new(user))
+              .joins("LEFT OUTER JOIN top_topics ON top_topics.topic_id = topics.id")
+              .joins("LEFT OUTER JOIN topic_users ON topic_users.topic_id = topics.id AND topic_users.user_id = #{user.id.to_i}")
               .where(closed: false, archived: false)
+              .where("COALESCE(topic_users.notification_level, 1) <> ?", TopicUser.notification_levels[:muted])
               .created_since(since)
               .listable_topics
-              .joins("LEFT OUTER JOIN top_topics ON top_topics.topic_id = topics.id")
               .order(TopicQuerySQL.order_top_for(score))
               .limit(100)