Charts don't support change from data to no data

In the situation where, for some reason, the chart data becomes undefined (after having data), the charts aren't properly discarding the previous render, keeping it. This may lead to the user trusting the data being shown which is not accurate.

It should, at least remove the existing data and show an empty chart. In the future, it should show a message saying "No Data Available" so the user knows why there's no chart rendered. The message feature will be tracked at HAWKULAR-962.