Improve model initialization and GPU handling in webui.py

- Add error handling for uninitialized model
- Ensure model is only initialized once
- Add GPU initialization logging
- Prevent redundant model loading

webui.py

@@ -52,8 +52,12 @@ def generate(text,
     global MODEL
     model = MODEL
     
+    if model is None:
+        raise RuntimeError("Model not initialized. Please ensure the model is loaded before generating audio.")
+    
     # if gpu available, move model to gpu
     if torch.cuda.is_available():
+        print("Moving model to GPU")
         model = model.to("cuda")
     
     with torch.no_grad():
@@ -111,11 +115,11 @@ def run_tts(
 
 def build_ui(model_dir, device=0):
     
-    # Initialize model
-    model = initialize_model(model_dir, device=device)
-    
     global MODEL
-    MODEL = model
+    
+    # Initialize model
+    if MODEL is None:
+        MODEL = initialize_model(model_dir, device=device)
 
     # Define callback function for voice cloning
     def voice_clone(text, prompt_text, prompt_wav_upload, prompt_wav_record):