Merge pull request #1 from cocos2d/develop

update cc2dx/develop
add check data valid in getStringFromFile

so far no check would be crashed when getData faild.
maybe return an empty string is better.
use data.isNull() instead of !data.getBytes()
Merge pull request #5070 from hbbalfred/develop

closed #3725: Crash if file doesn't exist when using FileUtils::getStringFromFile