shapeChecker.IsConvexPolygon: long thin rectangle is not a convex polygon

[HNeukermans]

executing following test fails: It's about a long thin rectangle 50 high and 1000 wide.

2 bugs:

• it is not recognized as convex
• is only has 3 corners instead of 4.

 public class SimpleShapeCheckerTest
{
        private List<IntPoint> rectangledTriangle = new List<IntPoint>();
        public SimpleShapeCheckerTest()
        {
            longThinRectangle.Add(new IntPoint(0, 0)); //corner
            longThinRectangle.Add(new IntPoint(20, 0));
            longThinRectangle.Add(new IntPoint(40, 0));
            longThinRectangle.Add(new IntPoint(50, 0)); //corner
            longThinRectangle.Add(new IntPoint(50, 100));
            longThinRectangle.Add(new IntPoint(50, 500));
            longThinRectangle.Add(new IntPoint(50, 1000)); // corner
            longThinRectangle.Add(new IntPoint(25, 1000));
            longThinRectangle.Add(new IntPoint(0, 1000));
            longThinRectangle.Add(new IntPoint(0, 500));
         }

         [TestMethod]
        public void IsConvexPolygon()
        {
            List<IntPoint> corners;
            Assert.AreEqual(true, shapeChecker.IsConvexPolygon(rectangle, out corners));
            Assert.AreEqual(4, corners.Count);
        }