ImagTimePropagation segfaults

Created by: twesterhout

The following code (on master branch) segfaults:

import netket
import numpy

hilbert = netket.hilbert.Spin(netket.graph.Hypercube(8, n_dim=1, pbc=True), s=0.5)
hamiltonian = netket.operator.Ising(h=1.0, hilbert=hilbert)
d = netket.exact.ImagTimePropagation(
    hamiltonian,
    netket.dynamics.create_timestepper(hilbert.n_states),
    0.0,
    numpy.random.rand(hilbert.n_states),
)
d.advance(200)

Even if some of the arguments are invalid, the code shouldn't segfault.