handle multiple returns properly in boxing wrappers (#42437)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/42437
Test Plan: Imported from OSS
Reviewed By: smessmer
Differential Revision: D22894191
Pulled By: bhosmer
fbshipit-source-id: fd4c7bc605a4b20bb3882f71e3b8874150671324
