Fix crash in GDI when empty rectangle

Source/Painting/SvgLinearGradientServer.cs

@@ -102,7 +102,7 @@ namespace Svg
                 };
 
                 var bounds = renderer.GetBoundable().Bounds;
-                if (bounds.Width <= 0 || bounds.Height <= 0) 
+                if (bounds.Width <= 0 || bounds.Height <= 0 || (points[0].X == points[1].X && (points[0].Y==points[1].Y))) 
                 {
                     if (this.GetCallback != null) return GetCallback().GetBrush(renderingElement, renderer, opacity, forStroke);
                     return null;