Genie in the OP image would've said "OK you now have 0 wishes".

Since he said 255, my interpretation is a valid solution.

Of course, if we're talking hypothetical wish gaining prevention methods, I'd just have a check before,

previous_wishes = wishes;

{Do all the wish things. wishes ends up with a 255 because of our shenanigans}

If(wishes>=previous_wishes) wishes = previous_wishes-1;

;If the current number of wishes isnt less than the old number of wishes, set it to the old number and subtract 1

If(wishes==0) {/*TODO: write function to end wish giving sequence*/}