added test for 0 valued radii

Author: derBobo

src/ImageSharp.Drawing/Shapes/EllipticalArcLineSegment.cs

@@ -37,8 +37,8 @@ public sealed class EllipticalArcLineSegment : ILineSegment
         /// <param name="transformation">The Tranformation matrix, that should be used on the arc.</param>
         public EllipticalArcLineSegment(float x, float y, float radiusX, float radiusY, float rotation, float startAngle, float sweepAngle, Matrix3x2 transformation)
         {
-            Guard.MustBeGreaterThan(radiusX, 0, nameof(radiusX));
-            Guard.MustBeGreaterThan(radiusY, 0, nameof(radiusY));
+            Guard.MustBeGreaterThanOrEqualTo(radiusX, 0, nameof(radiusX));
+            Guard.MustBeGreaterThanOrEqualTo(radiusY, 0, nameof(radiusY));
             this.x = x;
             this.y = y;
             this.radiusX = radiusX;

tests/ImageSharp.Drawing.Tests/Shapes/EllipticalArcLineSegmentTest.cs

@@ -19,5 +19,28 @@ public void ContainsStartandEnd()
             Assert.Equal(20, segment.EndPoint.X, 5);
             Assert.Equal(10, segment.EndPoint.Y, 5);
         }
+
+        [Fact]
+        public void checkZeroRadii()
+        {
+            IReadOnlyCollection<PointF> xRadiusZero = new EllipticalArcLineSegment(20, 10, 0, 20, 0, 0, 360, Matrix3x2.Identity).Flatten().ToArray();
+            IReadOnlyCollection<PointF> yRadiusZero = new EllipticalArcLineSegment(20, 10, 30, 0, 0, 0, 360, Matrix3x2.Identity).Flatten().ToArray();
+            IReadOnlyCollection<PointF> bothRadiiZero = new EllipticalArcLineSegment(20, 10, 0, 0, 0, 0, 360, Matrix3x2.Identity).Flatten().ToArray();
+            foreach (PointF point in xRadiusZero)
+            {
+                Assert.Equal(20, point.X);
+            }
+
+            foreach (PointF point in yRadiusZero)
+            {
+                Assert.Equal(10, point.Y);
+            }
+
+            foreach (PointF point in bothRadiiZero)
+            {
+                Assert.Equal(20, point.X);
+                Assert.Equal(10, point.Y);
+            }
+        }
     }
 }