{BugFix} Better support TEST scene

Summary:
TEST scenes comes with empty GT files for Hands and Object poses
- This diff improve supports when UmeTrack has been choosen as default option to show for HANDS

- JSONDecode can't take empty file as input

Reviewed By: fanzhangmeta

Differential Revision: D59923487

fbshipit-source-id: e6c5737e1228692f26f60395dde3e242dcb371f5

hot3d/data_loaders/UmeTrackHandDataProvider.py

@@ -72,7 +72,11 @@ def __init__(
         super()._init_hand_poses(hand_pose_trajectory_filepath)
 
         # Hand profile
-        self._hand_model = load_hand_model_from_file(hand_profile_filepath)
+        self._hand_model = (
+            None
+            if len(self._hand_poses) == 0
+            else load_hand_model_from_file(hand_profile_filepath)
+        )
 
     def get_hand_mesh_vertices(
         self, hand_wrist_data: HandPose