PLT-7092 Fixed creation of PostList with null Posts fields (#6924)

store/sql_channel_store.go

@@ -361,7 +361,7 @@ func (s SqlChannelStore) GetPinnedPosts(channelId string) StoreChannel {
 
 	go func() {
 		result := StoreResult{}
-		pl := &model.PostList{}
+		pl := model.NewPostList()
 
 		var posts []*model.Post
 		if _, err := s.GetReplica().Select(&posts, "SELECT * FROM Posts WHERE IsPinned = true AND ChannelId = :ChannelId AND DeleteAt = 0 ORDER BY CreateAt ASC", map[string]interface{}{"ChannelId": channelId}); err != nil {