FIX: permanent delete of posts by deleted users (#28992)

Permanently deleting posts that no longer have a user associated was not
working as expected because of UserAction.log which expected user_id to
be present.

app/services/user_action_manager.rb

@@ -60,8 +60,8 @@ class UserActionManager
   end
 
   def self.post_rows(post)
-    # first post gets nada
-    return [] if post.is_first_post? || post.topic.blank?
+    # first post gets nada or if the author has been deleted
+    return [] if post.is_first_post? || post.topic.blank? || post.user.blank?
 
     row = {
       action_type: UserAction::REPLY,

spec/lib/post_destroyer_spec.rb

@@ -1145,6 +1145,15 @@ RSpec.describe PostDestroyer do
       expect { regular_post.reload }.to raise_error(ActiveRecord::RecordNotFound)
       expect { topic.reload }.to raise_error(ActiveRecord::RecordNotFound)
     end
+
+    it "destroys the post when force_destroy is true for posts by deleted users" do
+      regular_post = Fabricate(:post, post_number: 2)
+      UserDestroyer.new(admin).destroy(regular_post.user, delete_posts: true)
+      regular_post.reload
+
+      PostDestroyer.new(moderator, regular_post, force_destroy: true).destroy
+      expect { regular_post.reload }.to raise_error(ActiveRecord::RecordNotFound)
+    end
   end
 
   describe "publishes messages to subscribers" do