MM-30048 added thread related socket messages (#16234)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

store/sqlstore/post_store.go

@@ -1976,7 +1976,7 @@ func (s *SqlPostStore) updateThreadsFromPosts(transaction *gorp.Transaction, pos
 		if thread, found := threadByRoot[rootId]; !found {
 			// calculate participants
 			var participants model.StringArray
-			if _, err := transaction.Select(&participants, "SELECT DISTINCT UserId FROM Posts WHERE RootId=:RootId", map[string]interface{}{"RootId": rootId}); err != nil {
+			if _, err := transaction.Select(&participants, "SELECT DISTINCT UserId FROM Posts WHERE RootId=:RootId OR Id=:RootId", map[string]interface{}{"RootId": rootId}); err != nil {
 				return err
 			}
 			// calculate reply count

store/storetest/thread_store.go

@@ -221,7 +221,7 @@ func testThreadStorePopulation(t *testing.T, ss store.Store) {
 		thread1, err := ss.Thread().Get(newPosts1[0].Id)
 		require.Nil(t, err)
 		require.EqualValues(t, thread1.ReplyCount, 1)
-		require.Len(t, thread1.Participants, 1)
+		require.Len(t, thread1.Participants, 2)
 
 		err = ss.Post().PermanentDeleteByUser(rootPost.UserId)
 		require.Nil(t, err)