Incorrect item width for OnItemClicked

[vsilux]

The width of the element to detect clicks on chart elements is calculated by the size of the entire chart widget. But when we use Y-axis decoration with showValues: true, the width of the chart decreases. Thus, the width of the element (bar) decreased. This causes a problem in _ChartWidget. _getClickLocation due to an incorrectly calculated item index that is forwards to: ChartBehavior._onChartItemClicked