Preserve Backward compatibility of models serialized before #31040 (#33796)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/33796
Test Plan: Imported from OSS
Differential Revision: D20109662
Pulled By: jerryzh168
fbshipit-source-id: 9bc936a59fd6dd1031fbf05eb90f98ae9677b936
