Fix Gradio Progress IndexError by using is not None

pipeline/rvc_training.py

@@ -55,7 +55,7 @@ def train_rvc_model(audio_path, model_name, epochs=100, batch_size=4, f0_method=
         return "Error: Please enter a model name.", None
 
     def p(val, desc):
-        if progress:
+        if progress is not None:
             progress(val, desc=desc)
         logger.info(desc)