Fix LTA error in Rat.base(1)
Fix LTA error in Rat.base(1)

Move check for base earlier, so we don't explode when we try to take .log(1)
of it. When (if) Num/x will follow IEEE rules, we can toss this check, since
there won't be any splosions with the log.

Fixes RT#130753: https://rt.perl.org/Ticket/Display.html?id=130753

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