proc: instance cell: missing bind for undeliverable messages (#511)

Summary:
Pull Request resolved: #511

i don't how this was overlooked but it seems to me this line of code is very obviously missing.

Reviewed By: mariusae

Differential Revision: D78180568

fbshipit-source-id: 62225c392f0d6118fa29b6c5f84765893ce1a6db

Author: shayne-fletcher

hyperactor/src/proc.rs

@@ -1519,8 +1519,9 @@ impl InstanceCell {
     /// We should find some (better) way to consolidate the two.
     pub(crate) fn bind<A: Actor, R: Binds<A>>(&self, ports: &Ports<A>) -> ActorRef<R> {
         <R as Binds<A>>::bind(ports);
-        // All actors handle signals:
+        // All actors handle signals and undeliverable messages.
         ports.bind::<Signal>();
+        ports.bind::<Undeliverable<MessageEnvelope>>();
         // TODO: consider sharing `ports.bound` directly.
         for entry in ports.bound.iter() {
             self.inner