Further micro-optimize List.roll($n)
Further micro-optimize List.roll($n)

- make decrementing part of the condition
- save the final todo value in the iterator

MasterDuke17/rakudo,nbrown/rakudo,tony-o/rakudo,nbrown/rakudo,Gnouc/rakudo,rakudo/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,labster/rakudo,labster/rakudo,tbrowder/rakudo,softmoth/rakudo,softmoth/rakudo,salortiz/rakudo,rakudo/rakudo,nbrown/rakudo,labster/rakudo,labster/rakudo,nbrown/rakudo,rakudo/rakudo,lucasbuchala/rakudo,tony-o/rakudo,tbrowder/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,tony-o/rakudo,salortiz/rakudo,salortiz/rakudo,lucasbuchala/rakudo,Gnouc/rakudo,MasterDuke17/rakudo,salortiz/rakudo,rakudo/rakudo,Gnouc/rakudo,Gnouc/rakudo,tony-o/rakudo,tony-o/rakudo,labster/rakudo,tony-o/rakudo,Gnouc/rakudo,MasterDuke17/rakudo,lucasbuchala/rakudo,softmoth/rakudo,tbrowder/rakudo,tbrowder/rakudo,lucasbuchala/rakudo,nbrown/rakudo,nbrown/rakudo,MasterDuke17/rakudo,lucasbuchala/rakudo,labster/rakudo,rakudo/rakudo,softmoth/rakudo,Gnouc/rakudo,salortiz/rakudo,salortiz/rakudo,softmoth/rakudo,rakudo/rakudo