Weaken check_cast_helper unavailable `from` type
Weaken check_cast_helper unavailable `from` type

Summary: D20088729 one up the stack re-organizes branches in a way that causes the type checker to report an inconsistency due to unavailable types. This diff addresses this lingering type checker problem, which exists independent of D20088729, and might cause builds to fail at any time.

Reviewed By: thezhangwei

Differential Revision: D20106209

fbshipit-source-id: 27c7f24e37be691e307068c1679065219e602e97

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex