Prevent divide-by-zero errors in Timer (#70050)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/66503
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70050
Reviewed By: mruberry
Differential Revision: D33168868
Pulled By: robieta
fbshipit-source-id: 7d0ece9e888f6c69a9e0ced581c92d3259fb3540
