FIX: Correctly publish messages unconditionally to admins (#13053)

Under certain conditions admins would miss messages when posting action in
topics where they have permission.

This also fixes an error where we would sometimes explode when publishing to
an empty group.

app/models/user_action.rb

@@ -283,14 +283,14 @@ class UserAction < ActiveRecord::Base
           update_like_count(user_id, hash[:action_type], 1)
         end
 
-        # move into Topic perhaps
         group_ids = nil
         if topic && topic.category && topic.category.read_restricted
-          group_ids = topic.category.groups.pluck("groups.id")
+          group_ids = [Group::AUTO_GROUPS[:admins]]
+          group_ids.concat(topic.category.groups.pluck("groups.id"))
         end
 
         if action.user
-          MessageBus.publish("/u/#{action.user.username.downcase}", action.id, user_ids: [user_id], group_ids: group_ids)
+          MessageBus.publish("/u/#{action.user.username_lower}", action.id, user_ids: [user_id], group_ids: group_ids)
         end
 
         action

spec/models/user_action_spec.rb

@@ -35,15 +35,18 @@ describe UserAction do
       }.merge(opts))
     end
 
-    describe "integration" do
-      before do
-        # Create some test data using a helper
-        log_test_action
-        log_test_action(action_type: UserAction::GOT_PRIVATE_MESSAGE)
-        log_test_action(action_type: UserAction::NEW_TOPIC, target_topic_id: public_topic.id, target_post_id: public_post.id)
-        log_test_action(action_type: UserAction::BOOKMARK)
+    it "allows publishing when group is deleted" do
+      public_topic.category.update!(read_restricted: true)
+
+      m = MessageBus.track_publish("/u/#{user.username_lower}") do
+        log_test_action(target_topic_id: public_topic.id, target_post_id: public_post.id)
       end
 
+      expect(m[0].group_ids).to eq([Group::AUTO_GROUPS[:admins]])
+      expect(m[0].user_ids).to eq([user.id])
+    end
+
+    describe "integration" do
       def stats_for_user(viewer = nil)
         UserAction.stats(user.id, Guardian.new(viewer)).map { |r| r.action_type.to_i }.sort
       end
@@ -53,6 +56,12 @@ describe UserAction do
       end
 
       it 'includes the events correctly' do
+        # Create some test data using a helper
+        log_test_action
+        log_test_action(action_type: UserAction::GOT_PRIVATE_MESSAGE)
+        log_test_action(action_type: UserAction::NEW_TOPIC, target_topic_id: public_topic.id, target_post_id: public_post.id)
+        log_test_action(action_type: UserAction::BOOKMARK)
+
         Jobs.run_immediately!
         PostActionNotifier.enable