replace v6 with experimental v7 code

src/MpvNet.Windows/WPF/HandyControl/Tools/Converter/BorderCircularConverter.cs

@@ -0,0 +1,32 @@
+
+
+using System.Globalization;
+using System.Windows;
+using System.Windows.Data;
+
+namespace HandyControl.Tools.Converter
+{
+    public class BorderCircularConverter : IMultiValueConverter
+    {
+        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
+        {
+            if (values.Length == 2 && values[0] is double width && values[1] is double height)
+            {
+                if (width < double.Epsilon || height < double.Epsilon)
+                {
+                    return new CornerRadius();
+                }
+
+                var min = Math.Min(width, height);
+                return new CornerRadius(min / 2);
+            }
+
+            return DependencyProperty.UnsetValue;
+        }
+
+        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
+        {
+            throw new NotSupportedException();
+        }
+    }
+}