Fix crash when posting a message to a send port with port id 0.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index c1b31428464d8f71ace98f290d306ceaae8d3b8f..5f4e4c23c99ce9d6fa06ce491a99323f6a1d55f0 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -20070,6 +20070,7 @@ void Capability::PrintJSONImpl(JSONStream* stream, bool ref) const {
 RawReceivePort* ReceivePort::New(Dart_Port id,
                                  bool is_control_port,
                                  Heap::Space space) {
+  ASSERT(id != ILLEGAL_PORT);
   Isolate* isolate = Isolate::Current();
   const SendPort& send_port =
       SendPort::Handle(isolate, SendPort::New(id, isolate->origin_id()));
@@ -20110,6 +20111,7 @@ RawSendPort* SendPort::New(Dart_Port id, Heap::Space space) {
 RawSendPort* SendPort::New(Dart_Port id,
                            Dart_Port origin_id,
                            Heap::Space space) {
+  ASSERT(id != ILLEGAL_PORT);
   SendPort& result = SendPort::Handle();
   {
     RawObject* raw = Object::Allocate(SendPort::kClassId,