Fixed a bug where WaveAuxiliaryField::assignValues was broken when using Dirichlet BC
Previously, only UnknownDofs where transferred from the auxiliary field to the multifield data buffer. When not all DOFs are unknown, it led to 1) index shifting that leads to wrong results 2) an insufficient amount of DOFs getting updated. Now, both known and unknown DOFs (and probably linked DOFs too, but untested) are properly exported.