fix normal with empty std (#66463)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/65709
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66463
Reviewed By: navahgar
Differential Revision: D31561904
Pulled By: ngimel
fbshipit-source-id: 3b2f44dc0ec075fe4f9685696578a0ff6e58d501
