Fix unnecessary pass by value
Fix unnecessary pass by value

ddemidov/amgcl,ddemidov/amgcl,dondieselkopf/amgcl,huahbo/amgcl,ddemidov/amgcl,huahbo/amgcl,ddemidov/amgcl,dondieselkopf/amgcl,huahbo/amgcl,dondieselkopf/amgcl