Merge branch 'master' of git://github.com/cocos2d/cocos2d-x
fixed UI animation stop cause crash
Merge branch 'master' of git://github.com/cocos2d/cocos2d-x
replace nullptr to NULL
Merge branch 'master' of git://github.com/cocos2d/cocos2d-x
Merge pull request #4320 from liamcindy/master

[ci skip]fixed ui anmation crash when stop animation for master