Fix test breakage caused by 48cc6b5

Implements:
- Channel.receive-nil-on-close
- Channel.iterator
- Channel.Seq
Re-Implements:
- Channel.list

Also: RT #127968 was a dup of RT #127960

src/core/Channel.pm

@@ -46,21 +46,28 @@ my class Channel {
         Nil
     }
 
-    method receive(Channel:D:) {
+    method !receive(Channel:D: $fail-on-close) {
         my \msg := nqp::shift($!queue);
         if nqp::istype(msg, CHANNEL_CLOSE) {
             nqp::push($!queue, msg);  # make sure other readers see it
             $!closed_promise_vow.keep(Nil);
             X::Channel::ReceiveOnClosed.new(channel => self).throw
+              if $fail-on-close;
+            Nil
         }
         elsif nqp::istype(msg, CHANNEL_FAIL) {
             nqp::push($!queue, msg);  # make sure other readers see it
             $!closed_promise_vow.break(msg.error);
             die msg.error;
         }
-        msg
+        else {
+            msg
+        }
     }
 
+    method receive(Channel:D:)              { self!receive(1) }
+    method receive-nil-on-close(Channel:D:) { self!receive(0) }
+
     method poll(Channel:D:) {
         my \msg := nqp::queuepoll($!queue);
         if nqp::isnull(msg) {
@@ -128,18 +135,21 @@ my class Channel {
         }
     }
 
-    multi method list(Channel:D:) {
-        Seq.new( class :: does Iterator {
+    method iterator(Channel:D:) {
+        class :: does Iterator {
             has $!channel;
             method !SET-SELF($!channel) { self }
             method new(\c) { nqp::create(self)!SET-SELF(c) }
             method pull-one() {
-                my Mu \got = $!channel.poll;
+                my Mu \got = $!channel.receive-nil-on-close;
                 nqp::eqaddr(got, Nil) ?? IterationEnd !! got
             }
-        }.new(self))
+        }.new(self)
     }
 
+    method Seq(Channel:D:)  { Seq.new(self.iterator) }
+    method list(Channel:D:) { self.Seq.list }
+
     method close() {
         $!closed = 1;
         nqp::push($!queue, CHANNEL_CLOSE);