message: fix wasserstein autodiff
diff: @@ -165,9 +165,9 @@ def wasserstein_distance(X, Y, matching=False, order=1., internal_p=np.inf, enab
  # empty arrays are not handled properly by the helpers, so we avoid calling them
  if len(pairs_X_Y):
  dists.append((Y_orig[pairs_X_Y[:, 1]] - X_orig[pairs_X_Y[:, 0]]).norms.lp(internal_p, axis=-1).norms.lp(order))
  - if len(pairs_X_diag):
  + if len(pairs_X_diag[0]):
  dists.append(_perstot_autodiff(X_orig[pairs_X_diag], order, internal_p))
  - if len(pairs_Y_diag):
  + if len(pairs_Y_diag[0]):
  dists.append(_perstot_autodiff(Y_orig[pairs_Y_diag], order, internal_p))
  dists = [dist.reshape(1) for dist in dists]
  return ep.concatenate(dists).norms.lp(order).raw
  