fix N=0 case in linear_forgetting_weights
fix N=0 case in linear_forgetting_weights

nicholas-leonard/hyperopt,beni55/hyperopt,jaberg/hyperopt,w1kke/hyperopt,466152112/hyperopt,mathkann/hyperopt,dallascard/hyperopt,CVML/hyperopt,allansp84/hyperopt,dudalev/hyperopt