message: UI-QT: fixed bug where selecting external magnetic field for visualisation would cause a crash.
diff: @@ -335,6 +335,8 @@ void SpinWidget::updateData()
  spins = System_Get_Spin_Directions(state.get());
  else if (this->m_source == 1)
  spins = System_Get_Effective_Field(state.get());
  + else
  + spins = System_Get_Spin_Directions(state.get());
  // copy
  /*positions.assign(spin_pos, spin_pos + 3*nos);
  directions.assign(spins, spins + 3*nos);*/
  