Use hrw validation function to validate netmap normalization

[alexvanin]

With nspcc-dev/hrw#7 we can use normalization check before HRW sorting. Something like this in GetSelection()

	if ss[0].Key == NodesBucket {
		if len(b.nodes) < count {
			return nil
		}

		nodes := make(Nodes, len(b.nodes))
		copy(nodes, b.nodes)
		if len(pivot) != 0 {
			w := nodes.Weights()
			if hrw.ValidateWeights(w) != nil {
				return nil
			}
			hrw.SortSliceByWeightValue(nodes, w, pivotHash)
		}
		root.nodes = nodes[:count]
		return &root
	}

[im-kulikov]

@alexvanin #7 is merged, mb we can close this issue?

[alexvanin]

@im-kulikov We can implement the proposal above or decline it. I proposed to do weight validation before HRW sorting.

if hrw.ValidateWeights(w) != nil {
	return nil
}
hrw.SortSliceByWeightValue(nodes, w, pivotHash)

Since this library contains explicit normalizers I think we can avoid any changes for extra weight validation. I think we can close this issue.