Update pfrl/utils/batch_states.py

The input feature type is checked better way.

Co-authored-by: Yasuhiro Fujita <muupan@gmail.com>

pfrl/utils/batch_states.py

@@ -31,6 +31,6 @@ def batch_states(
     features = [phi(s) for s in states]
     # return concat_examples(features, device=device)
     collated_features = default_collate(features)
-    if isinstance(collated_features, list):
+    if isinstance(features[0], tuple):
         collated_features = tuple(collated_features)
     return _to_recursive(collated_features, device)