Improve contour FindPointInPolygon() reliability (3).

src/Triangle.Tests/Geomerty/ContourTest.cs

@@ -63,5 +63,24 @@ namespace TriangleNet.Tests.Geometry
                 i = j;
             }
         }
+
+        [Test]
+        public void TestFindInteriorPointDup()
+        {
+            // Rectangle contour with duplicate point.
+            var points = new List<Vertex>()
+            {
+                new Vertex(0.0, 0.0),
+                new Vertex(0.0, 1.0),
+                new Vertex(2.0, 1.0),
+                new Vertex(2.0, 0.5),
+                new Vertex(2.0, 0.5), // duplicate
+                new Vertex(2.0, 0.0)
+            };
+
+            var contour = new Contour(points);
+
+            Assert.DoesNotThrow(() => contour.FindInteriorPoint());
+        }
     }
 }

src/Triangle/Tools/IntersectionHelper.cs

@@ -36,6 +36,9 @@ namespace TriangleNet.Tools
             // Length of the segment.
             double ab = (b.X - a.X) * (b.X - a.X) + (b.Y - a.Y) * (b.Y - a.Y);
 
+            // Ignore duplicate input points.
+            if (ab == 0) return false;
+
             // Check if test point is actually between a and b (right of b).
             if (dot > ab) return false;