DataLoader: add error detection for worker_init_fn (#20150)
Summary:
This is an attempt to isolate unrelated changes from #19228 for easier review.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20150
Differential Revision: D15314891
Pulled By: ezyang
fbshipit-source-id: 8c429747ba83ad5aca4cdd8f8086bcf65a326921
