Add possible fix

src/ImageSharp.Drawing/Processing/Processors/Drawing/FillRegionProcessor{TPixel}.cs

@@ -105,7 +105,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Drawing
 
                             QuickSort.Sort(buffer.Slice(0, pointsFound));
 
-                            for (int point = 0; point < pointsFound; point += 2)
+                            for (int point = 0; point < pointsFound && point < buffer.Length - 1; point += 2)
                             {
                                 // points will be paired up
                                 float scanStart = buffer[point] - minX;