Fix cluster-fuzz regression when getting message from Worker

test/mjsunit/regress/regress-crbug-504136.js

Index: test/mjsunit/regress/regress-crbug-504136.js
diff --git a/test/mjsunit/regress/regress-crbug-503698.js b/test/mjsunit/regress/regress-crbug-504136.js
similarity index 65%
copy from test/mjsunit/regress/regress-crbug-503698.js
copy to test/mjsunit/regress/regress-crbug-504136.js
index 274eb5a99e9bc392107d933400f1ff2a3aab0e13..0061ebd91db014a9d171fcf547d537c7d7a5ef1d 100644
--- a/test/mjsunit/regress/regress-crbug-503698.js
+++ b/test/mjsunit/regress/regress-crbug-504136.js
@@ -2,9 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --invoke-weak-callbacks
-
 if (this.Worker) {
-  function __f_1() {}
-  var __v_6 = new Worker(__f_1);
+  function __f_5() {}
+  var __v_10 = new Worker(__f_5);
+  __v_10.terminate();
+ __v_10.getMessage();
 }