Fixed wrong RoundRectangleGeometry calculation (#12286) fixes #12285

Author: jsuarezruiz

Xamarin.Forms.Controls/GalleryPages/ShapesGalleries/ClipGallery.xaml

@@ -41,6 +41,16 @@
                             Rect="0, 15, 150, 150" />
                     </Image.Clip>
                 </Image>
+                <Label
+                    Text="Clipped Image using RoundRectangleGeometry"/>
+                <Image  
+                    Source="crimson.jpg">
+                    <Image.Clip>
+                        <RoundRectangleGeometry
+                            CornerRadius="6"
+                            Rect="0, 15, 150, 150" />
+                    </Image.Clip>
+                </Image>
                 <Label
                     Text="Clipped Image using EllipseGeometry"/>
                 <Image  

Xamarin.Forms.Core/Shapes/RoundRectangleGeometry.cs

@@ -61,7 +61,7 @@ Geometry GetRoundRectangleGeometry()
 
 			if (CornerRadius.TopLeft > 0)
 				roundedRectGeometry.Children.Add(
-					new EllipseGeometry(new Point(Rect.Location.X + CornerRadius.TopLeft, Rect.Location.Y + CornerRadius.TopLeft), Rect.Location.Y + CornerRadius.TopLeft, Rect.Location.Y + CornerRadius.TopLeft));
+					new EllipseGeometry(new Point(Rect.Location.X + CornerRadius.TopLeft, Rect.Location.Y + CornerRadius.TopLeft), CornerRadius.TopLeft, CornerRadius.TopLeft));
 
 			if (CornerRadius.TopRight > 0)
 				roundedRectGeometry.Children.Add(