fix crash on torch.Tensor.repeat() for 0 repeats (#23766)
Summary:
This PR fixes https://github.com/pytorch/pytorch/issues/23603
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23766
Differential Revision: D16644866
Pulled By: soumith
fbshipit-source-id: ee7d368afdfe874133d0bd90f4d03a191ee22b13
