Zero Regularization strength should fall back to normal methods

Hi,

When using soft sorting or ranking with a 0 regularization, for the sake of convenience you should probably fall back to the normal sorting and ranking algorithm. Not sure how to do this in a clean way (that doesn't involve having soft stuff subclassing normal stuff).

In the meantime maybe you should raise at the init level if the strength (same as you did with the regularization type)?

