Don't use explicit return in dispatch:<::>
Don't use explicit return in dispatch:<::>

Fixes #3399 (for the JVM backend). Please note that MoarVM uses
different code for this purpose:
https://github.com/rakudo/rakudo/blob/add2ec0d49/src/vm/moar/spesh-plugins.nqp#L43-L44

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