FIX: Even more safety, the topic must exist as well.

app/models/topic_embed.rb

@@ -49,7 +49,7 @@ class TopicEmbed < ActiveRecord::Base
       absolutize_urls(url, contents)
       post = embed.post
       # Update the topic if it changed
-      if post && content_sha1 != embed.content_sha1
+      if post && && post.topic && content_sha1 != embed.content_sha1
         revisor = PostRevisor.new(post)
         revisor.revise!(user, absolutize_urls(url, contents), skip_validations: true, bypass_rate_limiter: true)
         embed.update_column(:content_sha1, content_sha1)