fix index out of range when only single point remains

fixes #16

src/SixLabors.Shapes/InternalPath.cs

@@ -200,6 +200,11 @@ namespace SixLabors.Shapes
         /// <returns>number of intersections hit</returns>
         public int FindIntersections(Vector2 start, Vector2 end, Vector2[] buffer, int count, int offset)
         {
+            if(this.points.Length < 2)
+            {
+                return 0;
+            }
+
             ClampPoints(ref start, ref end);
 
             var target = new Segment(start, end);

tests/SixLabors.Shapes.Tests/Issues/Issue_16.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Numerics;
+using System.Text;
+using Xunit;
+
+namespace SixLabors.Shapes.Tests
+{
+    /// <summary>
+    /// see https://github.com/SixLabors/Shapes/issues/16
+    /// Also for furter details see https://github.com/SixLabors/Fonts/issues/22 
+    /// </summary>
+    public class Issue_16
+    {
+        [Fact]
+        public void IndexOutoufRangeException()
+        {
+            var p = new InternalPath(new[] { new Vector2(0, 0), new Vector2(0.000000001f, 0), new Vector2(0, 0.000000001f) }, true);
+
+            var inter = p.FindIntersections(Vector2.One, Vector2.Zero);
+
+            // if simplified to single point then we should never have an intersection
+            Assert.Equal(0, inter.Count());
+        }
+    }
+}

tests/SixLabors.Shapes.Tests/PathExtensions.cs

@@ -23,19 +23,23 @@ namespace SixLabors.Shapes
         /// <returns>The points along the line the intersect with the boundaries of the polygon.</returns>
         internal static IEnumerable<Vector2> FindIntersections(this InternalPath path, Vector2 start, Vector2 end)
         {
+            List<Vector2> results = new List<Vector2>();
             var buffer = ArrayPool<Vector2>.Shared.Rent(path.PointCount);
             try
             {
                 var hits = path.FindIntersections(start, end, buffer, path.PointCount, 0);
                 for (var i = 0; i < hits; i++)
                 {
-                    yield return buffer[i];
+                    results.Add(buffer[i]);
                 }
             }
             finally
             {
                 ArrayPool<Vector2>.Shared.Return(buffer);
             }
+
+            return results;
         }
+
     }
 }