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

runtime/vm/dart_api_impl_test.cc

Index: runtime/vm/dart_api_impl_test.cc
diff --git a/runtime/vm/dart_api_impl_test.cc b/runtime/vm/dart_api_impl_test.cc
index b91fb1223aba96c80055e35d890568d4afa8deb9..306ca8832bf2f2b8f8ac6fa5af6ba687b5337243 100644
--- a/runtime/vm/dart_api_impl_test.cc
+++ b/runtime/vm/dart_api_impl_test.cc
@@ -7141,6 +7141,20 @@ void NewNativePort_send321(Dart_Port dest_port_id,
 }
 
 
+TEST_CASE(IllegalNewSendPort) {
+  Dart_Handle error = Dart_NewSendPort(ILLEGAL_PORT);
+  EXPECT(Dart_IsError(error));
+  EXPECT(Dart_IsApiError(error));
+}
+
+
+TEST_CASE(IllegalPost) {
+  Dart_Handle message = Dart_True();
+  bool success = Dart_Post(ILLEGAL_PORT, message);
+  EXPECT(!success);
+}
+
+
 UNIT_TEST_CASE(NewNativePort) {
   // Create a port with a bogus handler.
   Dart_Port error_port = Dart_NewNativePort("Foo", NULL, true);