Fix CUDA distributions test on Windows (#25539)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/25304.
The possible cause for the failure could have been the fact that `at::empty` was creating a tensor with very small values or 0, which led to `cumdist` not summing to a positive number.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25539
Differential Revision: D17156212
Pulled By: ezyang
fbshipit-source-id: ee8039e576bf76a2266aeb7e9537337d635e0f8f
