Zhujialing/调用component和child数组时加判断条件

[GeneralWar]

Re: cocos-creator/fireball#

Changelog:
*

Makes sure these boxes are checked before submitting your PR - thank you!

• If your pull request has gone "stale", you should rebase your work on top of the latest version of the upstream branch.
• If your commit history is full of small, unimportant commits (such as "fix pep8" or "update tests"), squash your commits down to a few, or one, discreet changesets before submitting a pull request.
• To official teams:
  • Check that your javascript is following our style guide and end files with a newline
  • Document new code with comments in source code based on API Docs
  • Make sure any runtime log information in cc.log , cc.error, cc.warn or cc.assert has been moved into DebugInfos.js with an ID

[gregwym]

缓存文件删掉。

[gregwym]

这个修改毋庸置疑是更安全的，但能否解释的通为何以前没有这个问题？是什么外界因素变化了才导致这里出现bug吗？