[PyTorch] Add tests for empty tensors w/storage null data_ptr (#101426)
Further investigation seems to show that changing this behavior (making empty tensors sometimes have non-null data_ptr) was the real problem with #98090 . Adding tests to lock down this behavior so we don't change it by accident again.
Differential Revision: [D45873002](https://our.internmc.facebook.com/intern/diff/D45873002/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101426
Approved by: https://github.com/zou3519
