The maximum number of moves seems to be infinite. In a sample of 1 million games, the maximum number of moves was 399; after 2 million, it was 437. Maybe there's an asymptote, I don't know. In any case, I think it is practically impossible to be that unlucky.
The maximum number of moves is infinite, provided sufficiently poor luck.
Proof: Starting on square 6, it is possible to spin an infinite sequence of fives, causing you to slide down the 16 -> 6 chute an infinite number of times and resulting in an infinite number of moves.
There are also several other infinite loops possible, due to the various chutes and the multiple sequences of spins that can take you from the bottom of any given chute to its top, but the 6-11-16 loop is the simplest to lay out.
(Disclaimer: I do not have a copy of the board readily available, so I have inferred the board topology from the posted source code. If there is no 16 -> 6 chute, or if there is a chute/ladder on 11, the specific example used will not work, but the general principle remains.)