iterator of a gridworld distribution can sometimes return an invalid state

[Zachary Sunberg]

function trans_mat(mdp::MDP, policy::Policy)
    n = n_states(mdp)
    T = spzeros(n, n)
    for s in iterator(states(mdp))
        i = state_index(mdp, s)
        tdist = transition(mdp, s, action(policy, s))
        for sp in iterator(tdist)
            j = state_index(mdp, sp)
            T[i,j] = pdf(tdist, sp)
        end
    end
    return T
end

pi = rand(actions(mdp), n_states(mdp));
Tpi = trans_mat(mdp, VectorPolicy(mdp, pi))

will produce this error

[Maxime]

this seems old