[3.2] set min/max value in UILoadingBar.setPercent

[hzlov]

Hey cocos2d-x team.

How about set min/max value instead of just return in setPercent() when value is out of range?

void LoadingBar::setPercent(float percent)
{
    if ( percent < 0 || percent > 100)
    {
        return;
    }
    ....
}