Get rid of "Uncaught exception in async net callback..."

Unity编辑器经常提示一个Warning：

Uncaught exception in async net callback: Object reference not set to an instance of an object
UnityEditor.AsyncHTTPClient:Done(State, Int32)

Unity的令人费解的BUG，解决方法为取消Show Asset Store search hits选项：

参考：http://blog.dreasgrech.com/2014/06/getting-rid-of-pesky-uncaught-exception.html