Fix cumprod error for tensors with zero elements (#32070)
Summary:
Currently cumprod crashes for tensors with non-empty dimensions but with zero elements, which could happen when some dimension is zero. This commit fixes the error by checking both dim() and numel() in cumprod backward
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32070
Differential Revision: D19373200
Pulled By: ezyang
fbshipit-source-id: d8ecde33f3330b40a7c611f6faa3b1d707ef2a9a
