[netcore] Make OverlappedTests.PackNegTest Pass #15308

System.NullReferenceException : Object reference not set to an instance of an object
      Stack Trace:
           at System.Threading.Overlapped.Pack(IOCompletionCallback iocb, Object userData)
           at OverlappedTests.PackNegTest()
           at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)