[estimation/sampler_nonrev] fix dirichlet sampling for non-pos alphas
[estimation/sampler_nonrev] fix dirichlet sampling for non-pos alphas

For states which have not been observed in the trajectory, or just once,
this sampling method failed for NumPy versions greater 1.13, because
the dirichlet function now checks for positive alphas.

In this fix we just omit these elements.

clonker/ci-tests