Add defensive NaN checks for Canvas position values in eraser tool

Co-authored-by: RuntimeRascal <2422222+RuntimeRascal@users.noreply.github.com>

Author: Copilot

Src/GhostDraw/Tools/EraserTool.cs

@@ -141,23 +141,35 @@ private void EraseAtPosition(Point position, Canvas canvas)
                     // Check if eraser intersects with rectangle bounds
                     double left = Canvas.GetLeft(rectangle);
                     double top = Canvas.GetTop(rectangle);
-                    Rect shapeRect = new Rect(left, top, rectangle.Width, rectangle.Height);
 
-                    if (eraserRect.IntersectsWith(shapeRect))
+                    // Handle NaN values (shouldn't happen, but be defensive)
+                    if (!double.IsNaN(left) && !double.IsNaN(top) && 
+                        !double.IsNaN(rectangle.Width) && !double.IsNaN(rectangle.Height))
                     {
-                        shouldErase = true;
+                        Rect shapeRect = new Rect(left, top, rectangle.Width, rectangle.Height);
+                        
+                        if (eraserRect.IntersectsWith(shapeRect))
+                        {
+                            shouldErase = true;
+                        }
                     }
                 }
                 else if (element is Ellipse ellipse)
                 {
                     // Check if eraser intersects with ellipse bounds
                     double left = Canvas.GetLeft(ellipse);
                     double top = Canvas.GetTop(ellipse);
-                    Rect ellipseRect = new Rect(left, top, ellipse.Width, ellipse.Height);
 
-                    if (eraserRect.IntersectsWith(ellipseRect))
+                    // Handle NaN values (shouldn't happen, but be defensive)
+                    if (!double.IsNaN(left) && !double.IsNaN(top) && 
+                        !double.IsNaN(ellipse.Width) && !double.IsNaN(ellipse.Height))
                     {
-                        shouldErase = true;
+                        Rect ellipseRect = new Rect(left, top, ellipse.Width, ellipse.Height);
+                        
+                        if (eraserRect.IntersectsWith(ellipseRect))
+                        {
+                            shouldErase = true;
+                        }
                     }
                 }