FIX: Allow editing post that belongs to deleted topic

app/services/post_action_notifier.rb

@@ -97,6 +97,7 @@ class PostActionNotifier
     return unless post
     return if post_revision.user.blank?
     return if post_revision.user_id == post.user_id
+    return if post.topic.blank?
     return if post.topic.private_message?
     return if SiteSetting.disable_edit_notifications && post_revision.user_id == Discourse::SYSTEM_USER_ID