Fix wrong handling of `grad_scale` & `found_inf` in fused optimizers (#95847)
Fixes #95781.
The cause seems to be that the current implementation doesn't correctly pass `found_inf` when `grad_scale` is `None`. Therefore parameters can get mistakenly updated by gradients whose some elements are invalid, i.e. nan or inf.
Related #94060
I forgot about this wrong handling after #94344
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95847
Approved by: https://github.com/janeyx99
