CombinedChartView: First and last bars are shown half only

I migrated my existing code to Charts 3.0.1 now and have some issues with the combined chart view (bars and lines).

After the straight forward migration my diagram looks as shown in the following picture.

When I add the following lines of code in order to show the bars completely the xAxis values gets corrupted completely.

``` Swift
combChart.xAxis.granularityEnabled = true
combChart.xAxis.granularity = 1.0
combChart.xAxis.spaceMin = 0.5
combChart.xAxis.spaceMax = 0.5
combChart.xAxis.valueFormatter = self
```


The Strings for the xAxis values are drawn with the following lines of code.

``` Swift
public func stringForValue(_ value: Double, axis: AxisBase?) -> String
{
if Int(value) < _xValues.count {
return _xValues[Int(value)]
} else {
return ""
}
}
```

I checked the output the `stringForValue`function. But the function gets called exactly 4 times and returns the correct Strings:

```
2017.01.22 11:23:43.460 [DEBUG] [DiagramCombinedCollectionViewCell stringForValue(_:axis:)](417): xValue: 0.000000 1. Serie
2017.01.22 11:23:43.461 [DEBUG] [DiagramCombinedCollectionViewCell stringForValue(_:axis:)](417): xValue: 1.000000 2. Serie
2017.01.22 11:23:43.462 [DEBUG] [DiagramCombinedCollectionViewCell stringForValue(_:axis:)](417): xValue: 2.000000 3. Serie
2017.01.22 11:23:43.463 [DEBUG] [DiagramCombinedCollectionViewCell stringForValue(_:axis:)](417): xValue: 3.000000 4. Serie
```

Any idea whats going wrong? Or do I forget to set any relevant axis parameter?

Start by reproducing the CombinedChartView with the reported bar and xAxis settings, then trace how the xAxis values and bar boundaries are rendered. Use the provided stringForValue implementation and logged values to compare label positions with the displayed chart; done means both end bars are fully visible and the four xAxis labels remain correct.

Written by the indexing model from the issue text.