Fix a bug.

app.py

@@ -60,7 +60,7 @@ def predict(
     resolution: str,
     weights_file: Optional[str]
 ) -> Tuple[np.ndarray, np.ndarray]:
-    # global birefnet
+    global birefnet
     # Load BiRefNet with chosen weights
     _weights_file = '/'.join(('zhengpeng7', usage_to_weights_file[weights_file] if weights_file is not None else usage_to_weights_file['General']))
     print('Using weights:', _weights_file)
@@ -94,6 +94,8 @@ def predict(
     pred = np.repeat(np.expand_dims(pred, axis=-1), 3, axis=-1)
     image_pred = (pred * np.array(image_pil)).astype(np.uint8)
 
+    torch.cuda.empty_cache()
+
     return image, image_pred