Fix off-by-one error in Supply.head(limit)
Fix off-by-one error in Supply.head(limit)

- limit 0 would give all emittees
- limit <0 would also give all emittees

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