Be a more careful about interesting indexes
Be a more careful about interesting indexes

Backtrace.next-interesting-index *can* return Nil, so we should guard
against that by remembering the last valid index.

usev6/rakudo,nbrown/rakudo,raydiak/rakudo,tony-o/rakudo,softmoth/rakudo,salortiz/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,awwaiid/rakudo,jonathanstowe/rakudo,tony-o/rakudo,tbrowder/rakudo,rakudo/rakudo,nbrown/rakudo,usev6/rakudo,rakudo/rakudo,sjn/rakudo,Gnouc/rakudo,lucasbuchala/rakudo,jonathanstowe/rakudo,softmoth/rakudo,lucasbuchala/rakudo,Gnouc/rakudo,sjn/rakudo,labster/rakudo,Gnouc/rakudo,awwaiid/rakudo,labster/rakudo,awwaiid/rakudo,MasterDuke17/rakudo,rakudo/rakudo,softmoth/rakudo,rakudo/rakudo,labster/rakudo,raydiak/rakudo,tbrowder/rakudo,tony-o/rakudo,salortiz/rakudo,softmoth/rakudo,tony-o/rakudo,tony-o/rakudo,Gnouc/rakudo,sjn/rakudo,nbrown/rakudo,jonathanstowe/rakudo,salortiz/rakudo,sjn/rakudo,lucasbuchala/rakudo,MasterDuke17/rakudo,nbrown/rakudo,tony-o/rakudo,softmoth/rakudo,rakudo/rakudo,Gnouc/rakudo,tbrowder/rakudo,salortiz/rakudo,nbrown/rakudo,salortiz/rakudo,usev6/rakudo,jonathanstowe/rakudo,MasterDuke17/rakudo,awwaiid/rakudo,labster/rakudo,labster/rakudo,sjn/rakudo,awwaiid/rakudo,labster/rakudo,lucasbuchala/rakudo,lucasbuchala/rakudo,rakudo/rakudo,raydiak/rakudo,jonathanstowe/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,usev6/rakudo,tbrowder/rakudo,usev6/rakudo,salortiz/rakudo,raydiak/rakudo,Gnouc/rakudo,nbrown/rakudo,MasterDuke17/rakudo