Zero round (joker output)

A zero round appears at the Solitaire algorithm always , if in step 5 of the keystream generation a joker is found.
In this case the card value 53 (at a card deck consisting of 54 cards) is not taken as the keystream letter, but the algorithm is started again, until a valid card value (1-52) is found in step 5.

This is leaded of the application impliedly.