Make List.join on empty lists 2x as fast
Make List.join on empty lists 2x as fast

And half the number of allocations.  Basically doesn't initialize
$!reified if it is not needed.

rakudo/rakudo,sjn/rakudo,lucasbuchala/rakudo,zostay/rakudo,sjn/rakudo,nbrown/rakudo,sjn/rakudo,b2gills/rakudo,jonathanstowe/rakudo,Gnouc/rakudo,tony-o/rakudo,zostay/rakudo,rakudo/rakudo,samcv/rakudo,awwaiid/rakudo,tbrowder/rakudo,softmoth/rakudo,softmoth/rakudo,zostay/rakudo,MasterDuke17/rakudo,softmoth/rakudo,tony-o/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,usev6/rakudo,raydiak/rakudo,salortiz/rakudo,nbrown/rakudo,MasterDuke17/rakudo,usev6/rakudo,samcv/rakudo,tony-o/rakudo,lucasbuchala/rakudo,sjn/rakudo,labster/rakudo,zostay/rakudo,Gnouc/rakudo,lucasbuchala/rakudo,awwaiid/rakudo,Gnouc/rakudo,usev6/rakudo,softmoth/rakudo,softmoth/rakudo,b2gills/rakudo,samcv/rakudo,rakudo/rakudo,nbrown/rakudo,nbrown/rakudo,labster/rakudo,salortiz/rakudo,nbrown/rakudo,awwaiid/rakudo,Gnouc/rakudo,labster/rakudo,salortiz/rakudo,tony-o/rakudo,lucasbuchala/rakudo,b2gills/rakudo,tony-o/rakudo,awwaiid/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,usev6/rakudo,samcv/rakudo,salortiz/rakudo,rakudo/rakudo,b2gills/rakudo,raydiak/rakudo,rakudo/rakudo,nbrown/rakudo,jonathanstowe/rakudo,raydiak/rakudo,tbrowder/rakudo,usev6/rakudo,sjn/rakudo,samcv/rakudo,Gnouc/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,Gnouc/rakudo,tbrowder/rakudo,labster/rakudo,salortiz/rakudo,labster/rakudo,tony-o/rakudo,tbrowder/rakudo,jonathanstowe/rakudo,jonathanstowe/rakudo,lucasbuchala/rakudo,raydiak/rakudo,labster/rakudo,rakudo/rakudo,b2gills/rakudo,jonathanstowe/rakudo,awwaiid/rakudo,salortiz/rakudo