[BarChart] single dataSet + force groupSpace=0.8 leads to wrong xAxis label rendering and highlight

[liuxuan30]

Bar chart with single dataSet and force groupSpace to be 0.8 will leads to strange behavior for xAxis label rendering and highlight when scaleX > 1.0.

To reproduce, simply return a number say 0.8 for groupSpace, like below, and zoom in and scroll, you will see some xAxis label disappeared, and highlighting also highlight wrong bar.

    /// The spacing is relative to a full bar width
    public var groupSpace: CGFloat
    {
        get
        {
            if (_dataSets.count <= 1)
            {
                return 0.8
            }
            return _groupSpace
        }
        set
        {
            _groupSpace = newValue
        }
    }

I am not sure if it's intended to return groupSpace 0.0 for single dataSet. It seems like we don't want to support groupSpace for single dataSet?

[liuxuan30]

Closing as with single dataSet we should use barSpace directly.