Update app.py

app.py

@@ -28,6 +28,7 @@ model = None
 @spaces.GPU(duration=120)
 def process_json_and_generate_audio(prompt_audio_role0_file, prompt_text_role0, prompt_audio_role1_file, prompt_text_role1, json_dialogue_input_str):
     try:
+        global model
         if model is None:
             model = Model()
             model.generate_config.max_new_tokens = 50 * 50 # no more than 20s per turn