[C2] Fixed a bug in normalization operator (#40925)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40925
normalization operator does not handle empty tensors correctly. This is a fix.
Test Plan: unit tests
Differential Revision: D22330340
fbshipit-source-id: 0bccf925bb768ebb997ed0c88130c5556308087f
