[PCS] skip npos in creating Dirichlet BC

ProcessLib/BoundaryCondition/DirichletBoundaryCondition.cpp

@@ -45,6 +45,8 @@ void DirichletBoundaryCondition::getEssentialBCValues(
         // TODO: that might be slow, but only done once
         const auto g_idx =
             _dof_table.getGlobalIndex(l, _variable_id, _component_id);
+        if (g_idx == NumLib::MeshComponentMap::nop)
+            continue;
         // For the DDC approach (e.g. with PETSc option), the negative
         // index of g_idx means that the entry by that index is a ghost one,
         // which should be dropped. Especially for PETSc routines MatZeroRows