vdc --vtk, repeats the first spin multiple times in the vtu output

[mahdawi]

vdc --vtk copies the first spin "num_atoms" times, then it starts adding the remaining spins. It seems the issue is from "vdc::atoms_list". Replacing it by "sliced_atoms_list" on lines 69, 72 solves the issue.

- for(size_t i=0; i < vdc::atoms_list.size(); i++){
+ for(size_t i=0; i < vdc::sliced_atoms_list.size(); i++){
- unsigned int atom = vdc::atoms_list[i];
+ unsigned int atom = vdc::sliced_atoms_list[i];