addmm: Fix handling of case with empty tensor (#28613)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28613
addmm: Fix handling of case with empty tensor.
Currently these cause an error
Recreation of D18085389 without stacked diffs
Test Plan: test included
Differential Revision: D18122004
fbshipit-source-id: 71513c02ace691902553bea5ce9dc2538cca4c99
