Fix tap add/remove race in Supplier
Fix tap add/remove race in Supplier

This applies a similar fix as was done to Supplier::Preserving in
68d79e70fb. This may well resolve #2224.

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