[optim] bugfix when all parameters have no grad (#52944)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52944
This fix the bug introduced during refactoring optimizers https://github.com/pytorch/pytorch/pull/50411. When all parameters have no grads, we should still allows `beta` like hyper params to be defined.
Reviewed By: ngimel
Differential Revision: D26699827
fbshipit-source-id: 8a7074127704c7a4a1fbc17d48a81e23a649f280
