fix using -1 in getitem for stores
fix using -1 in getitem for stores

openpathsampling/openpathsampling,dwhswenson/openpathsampling,choderalab/openpathsampling,openpathsampling/openpathsampling,openpathsampling/openpathsampling,dwhswenson/openpathsampling,dwhswenson/openpathsampling,choderalab/openpathsampling,jhprinz/openpathsampling,openpathsampling/openpathsampling,choderalab/openpathsampling,jhprinz/openpathsampling,jhprinz/openpathsampling,dwhswenson/openpathsampling