Fix incorrect underflow detection in infix:<**>
Fix incorrect underflow detection in infix:<**>

Introed in previous commit[^1].
Since we negate the power, we'd get an Inf on too large
power, not 0e0.

[1] https://github.com/rakudo/rakudo/commit/d1729da26a8a2e869d87549d1cb4c6075d38d55f

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