[Bug] Unhandled ArgumentNullException rendering charts

[mfeingol]

Describe the bug
Same issue as #193

An unhandled exception occurs rendering charts on Windows UWP. This issue occurs with 0.9.5.9 and 1.0.0.0-preview. It does not occur with 0.7.1. I would love to see an official or even preview release that has a fix for this.

System.ArgumentNullException: Value cannot be null.
Parameter name: text
   at SkiaSharp.SKCanvas.DrawText(String text, Single x, Single y, SKFont font, SKPaint paint)
   at Microcharts.PointChart.DrawLabels(SKCanvas canvas, String[] texts, SKPoint[] points, SKRect[] sizes, SKColor[] colors, Orientation orientation, Boolean isTop, SKSize itemSize, Single height)
   at Microcharts.PointChart.DrawFooter(SKCanvas canvas, String[] labels, SKRect[] labelSizes, SKPoint[] points, SKSize itemSize, Int32 height,

Which platform and version is this for?
Windows UWP

To Reproduce
cf #193

Expected behavior
No unhandled exceptions