bug in base point insertion strategy

https://github.com/tremlin/PermLib/blob/2b4e468e24a059e3659bc095293df0cd363a22f5/include/permlib/redundant_base_point_insertion_strategy.h#L78

This seems to be a bug: the type of i is `unsigned int`, so what's the intended action of calculating -i-1? This actually throws an error in MSVCC.