[fix] torch.multinomial : fix for 0 size dim (#43775)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/43768
TO-DO:
* [x] Add test
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43775
Reviewed By: ZolotukhinM
Differential Revision: D23421979
Pulled By: ngimel
fbshipit-source-id: 949fcdd30f18d17ae1c372fa6ca6a0b8d0d538ce
