fix segfault in torch.native_channel_shuffle when input is empty (#121199)
Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at bottom):
fix https://github.com/pytorch/pytorch/issues/121092
`torch.channel_shuffle` could handle empty inputs correctly. `torch.native_channel_shuffle` bypassed the `numel == 0` check, this causes divided by zero in underlying kernel.
* __->__ #121199
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121199
Approved by: https://github.com/malfet
