text: Title: 在运行官方给的Advanced Usage示例时报错
  Body: 运行Basic Usage没有问题，但运行Advanced Usage时出现以下报错
  
  Traceback (most recent call last):
    File "xxx/test1.py", line 10, in <module>
      rand_spk = chat.sample_random_speaker()
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "xxx/ChatTTS/ChatTTS/core.py", line 160, in sample_random_speaker
      return self.speaker.sample_random()
             ^^^^^^^^^^^^
  AttributeError: 'Chat' object has no attribute 'speaker'
  
  ![屏幕截图 2024-10-21 154855](https://github.com/user-attachments/assets/841db745-ee6a-4ff0-8991-93a6001a804b)