[BugFix] Fix unlock in RB (#1135)

Author: vmoens

torchrl/data/replay_buffers/storages.py

@@ -276,7 +276,8 @@ def get(self, index: Union[int, Sequence[int], slice]) -> Any:
         out = self._storage[index]
         if is_tensor_collection(out):
             out = _reset_batch_size(out)
-        return out.unlock_()
+            return out.unlock_()
+        return out
 
     def __len__(self):
         return self._len