Add error handling

app.py

@@ -498,7 +498,8 @@ def delete_last_drag(tracking_points, first_frame_path, drag_mode):
  color = (255, 0, 0, 255)
  elif drag_mode == "camera":
  color = (0, 0, 255, 255)
- tracking_points.pop()
+ if tracking_points:
+ tracking_points.pop()
  transparent_background = Image.open(first_frame_path).convert("RGBA")
  w, h = transparent_background.size
  transparent_layer = np.zeros((h, w, 4))