Fix typo error of X11Window ClientMessageEvent.ptr5 (#19439)

src/Avalonia.X11/X11Window.cs

@@ -1245,10 +1245,10 @@ namespace Avalonia.X11
                     ptr1 = l0,
                     ptr2 = l1 ?? IntPtr.Zero,
                     ptr3 = l2 ?? IntPtr.Zero,
-                    ptr4 = l3 ?? IntPtr.Zero
+                    ptr4 = l3 ?? IntPtr.Zero,
+                    ptr5 = l4 ?? IntPtr.Zero
                 }
             };
-            xev.ClientMessageEvent.ptr4 = l4 ?? IntPtr.Zero;
             XSendEvent(_x11.Display, _x11.RootWindow, false,
                 new IntPtr((int)(EventMask.SubstructureRedirectMask | EventMask.SubstructureNotifyMask)), ref xev);