Assert tensor isn't sparse in enforce_invariants. (#18338)
Summary:
There's no reason we can't check this, but I'm punting on implementing it for now. But it currently segfaults, so this is an improvements.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18338
Differential Revision: D14580308
Pulled By: gchanan
fbshipit-source-id: 44d4cafeab12e1beeb3453a2d4068d221c2e9c4f
