Fix fallback graph in specialize autogradzero (#44654)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44654
Previously we weren't creating a fallback graph as intended in specialize autograd zero, so if a Tensor failed one of our undefinedness checks we would run the backward normally without reprofiling & optimizing.
Test Plan: Imported from OSS
Reviewed By: jamesr66a
Differential Revision: D23691764
Pulled By: eellison
fbshipit-source-id: 10c6fa79518c84a6f5ef2bfbd9ea10843af751eb
