Issue #2829: fixed a bug of WebAudioEngine that it's effect can't stop/pause when the effect didn't preload.
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss2829_ImproveAudioCompatibility
Merge pull request #1259 from dingpinglv/Iss2829_ImproveAudioCompatibility

Issue #2829: fixed a bug of WebAudioEngine that it's effect can't stop/pause when the effect didn't preload.