hparams : add check for layer index in is_recurrent (#16511)
* hparams : add check for layer index in is_recurrent
This commit adds a check in the is_recurrent method to ensure that the
provided layer index is within the valid range.
The motivation for this change is to prevent potential out-of-bounds
and also be consistent with other methods in the class that perform
similar checks, like is_swa.
