[PL] fix process var move ctor

ProcessLib/ProcessVariable.cpp

@@ -98,6 +98,7 @@ ProcessVariable::ProcessVariable(BaseLib::ConfigTree const& config,
 ProcessVariable::ProcessVariable(ProcessVariable&& other)
     : _name(std::move(other._name)),
       _mesh(other._mesh),
+      _n_components(other._n_components),
       _initial_condition(std::move(other._initial_condition)),
       _dirichlet_bc_configs(std::move(other._dirichlet_bc_configs)),
       _neumann_bc_configs(std::move(other._neumann_bc_configs))

ProcessLib/ProcessVariable.h

@@ -104,7 +104,7 @@ public:
 private:
 	std::string const _name;
 	MeshLib::Mesh& _mesh;
-	int _n_components;
+	const int _n_components;
 	std::unique_ptr<InitialCondition> _initial_condition;
 	std::vector<std::unique_ptr<UniformDirichletBoundaryCondition>>
 	    _dirichlet_bc_configs;