Add assert to ensure the divisor is not 0 (#25960)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25960
Pull Request resolved: https://github.com/pytorch/FBGEMM/pull/124
Test Plan: CI
Reviewed By: dskhudia
Differential Revision: D17292372
fbshipit-source-id: 71a72f87b99c65b3b956bd8361694b1de05fc333
