Fixes bugs in torch.multinomial without replacement (#22183)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22183
ghimport-source-id: f03c17178de115adbe983953a8f9f205e3df7721
Test Plan: Imported from OSS
Differential Revision: D15985324
Pulled By: ezyang
fbshipit-source-id: 6e9dc3b54d448f4bb374b004d7f1dd1ac5c014f6
