message: Bugfix in core: n_shells = 0.
  Exchange and DMI n_shells is now checked before logging, preventing a crash when n=0.
diff: @@ -969,8 +969,10 @@ namespace Utility
  Log(Log_Level::Parameter, Log_Sender::IO, " K from file");
  Log(Log_Level::Parameter, Log_Sender::IO, " K_normal[0] = " + std::to_string(K_normal[0]) + " " + std::to_string(K_normal[1]) + " " + std::to_string(K_normal[2]));
  Log(Log_Level::Parameter, Log_Sender::IO, " n_shells_exchange = " + std::to_string(n_neigh_shells_exchange));
  + if (n_neigh_shells_exchange > 0)
  Log(Log_Level::Parameter, Log_Sender::IO, " J_ij[0] = " + std::to_string(jij[0]));
  Log(Log_Level::Parameter, Log_Sender::IO, " n_shells_dmi = " + std::to_string(n_neigh_shells_dmi));
  + if (n_neigh_shells_dmi > 0)
  Log(Log_Level::Parameter, Log_Sender::IO, " D_ij[0] = " + std::to_string(dij[0]));
  Log(Log_Level::Parameter, Log_Sender::IO, " DM chirality = " + std::to_string(dm_chirality));
  Log(Log_Level::Parameter, Log_Sender::IO, " dd_radius = " + std::to_string(dd_radius));
  