fix error in arcTo.

Runtime/ui/painting/path.cs

                     while (da < 0.0f) {
                         da += Mathf.PI * 2;
                     }
+                    if (da <= 1e-5) {
+                        return new List<float>();
+                    }
                 }
             } else {
                 if (Mathf.Abs(da) >= Mathf.PI * 2) {
                         da -= Mathf.PI * 2;
+                    }
+                    if (da >= -1e-5) {
+                        return new List<float>();
                     }
                 }
             }
             }
 
             var points = TessellationGenerator.tessellateBezier(x1, y1, x2, y2, x3, y3, x4, y4, this._tessTol);
+            D.assert(points.Count > 0);
+            Debug.Log(points.Count + $"{x1} {y1} {x2} {y2} {x3} {y3} {x4} {y4}");
+            
             points[points.Count - 1].flags = flags;
             foreach (var point in points) {
                 this._addPoint(point);