Closed #5375: fixed a bug of cc._audioLoader that it doesn't work when a audio file loads fail.
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss5375_AudioLoader
Merge pull request #1883 from dingpinglv/Iss5375_AudioLoader

Closed #5375: fixed a bug of cc._audioLoader that it doesn't work when a audio file loads fail.