Fix reading `__cuda_array_interface__` without strides (#24947)
Summary:
When converting a contiguous CuPy ndarray to Tensor via `__cuda_array_interface__`, an error occurs due to incorrect handling of default strides. This PR fixes this problem. It makes `torch.tensor(cupy_ndarray)` works for contiguous inputs.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24947
Differential Revision: D18838986
Pulled By: ezyang
fbshipit-source-id: 2d827578f54ea22836037fe9ea8735b99f2efb42
