[torchbind] Better error message when missing init. (#37474)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37474
Previously we would segfault
Test Plan: Imported from OSS
Differential Revision: D21297542
Pulled By: suo
fbshipit-source-id: c7e2f828a250c490ec23fb51c6a4a642d3370e52
