Fixed a bug in aggregation
Fixed a bug in aggregation

The bug only showed itself when openmp was not available

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