max_pool_with_indices: return valid indices if all input elements are -inf (#23161)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/20465.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23161
Differential Revision: D16442672
Pulled By: ezyang
fbshipit-source-id: 8c2ee13acd73954c7307720c01c732f460266a63
