hidden percent and max information in ProgressBar sample fixes #301

Thought this was the easiest way to fix #301. Tell me what you think.
I'm not sure what your mean but NaN is a normal value for ProgressBar, [it's documented](https://github.com/ibm-js/deliteful/blob/f19f608b95fd642e02d3b62e1e29f5caab6c18af/docs/ProgressBar.md#determinate-vs-indeterminate).

As for why the 'change' event is fired (calling the handler), I looked a little into that and it seems to come from the [notifyCurrentValue calls](https://github.com/ibm-js/deliteful/blob/master/ProgressBar.js#L165) in post render phase.