Improve zero sized input for addmv (#41824)
Summary:
fixes https://github.com/pytorch/pytorch/issues/41340
Unfortunately, I still can not get a K80 to verify the fix, but it should be working.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41824
Reviewed By: mruberry
Differential Revision: D23172775
Pulled By: ngimel
fbshipit-source-id: aa6af96fe74e3bb07982c006cb35ecc7f18181bc
