Prevent NullReferenceException in LayoutButton

[GamesAgeddon]

• ICrossPlatformLayout.CrossPlatformArrange can call LayoutButton with a null button so it should be prepared for that.

Fixes #31048

[github-actions]

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curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 35284

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[dotnet-policy-service]

Hey there @@GamesAgeddon! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[kubaflo]

Hi! Can you create a test for it to prove the bug?

[GamesAgeddon]

@kubaflo It's very hard to reproduce in a real app. I need around 5 to 15 minutes every time navigating back and forth in our app, hoping that the timing causes this issue. In a test scenario, you can force it with these lines of code in any project targeting net10.0-ios.

var b = new Button();
((ICrossPlatformLayout)b).CrossPlatformArrange(Rect.Zero);

Because as seen in the screenshot Size ICrossPlatformLayout.CrossPlatformArrange handle safely if the handler is null var platformButton = Handler?.PlatformView as UIButton; but just call LayoutButton, which is not prepared for it, we see this exception.

[System.NullReferenceException thrown]	
>	Microsoft.Maui.Controls.dll!Microsoft.Maui.Controls.Button.LayoutButton(UIKit.UIButton platformButton, Microsoft.Maui.Controls.Button button, Microsoft.Maui.Graphics.Rect size) Line 186	C#
 	Microsoft.Maui.Controls.dll!Microsoft.Maui.Controls.Button.Microsoft.Maui.ICrossPlatformLayout.CrossPlatformArrange(Microsoft.Maui.Graphics.Rect bounds) Line 165	C#
 	CustomApp.Maui.iOS.dll!CustomApp.Maui.iOS.Handlers.IosButtonHandler.TryGetPlatformView(CustomApp.Maui.iOS.Handlers.IosButtonHandler handler) Line 68	C#
 	CustomApp.Maui.iOS.dll!CustomApp.Maui.iOS.Handlers.IosButtonHandler.PlatformArrange(Microsoft.Maui.Graphics.Rect rect) Line 28	C#
 	Microsoft.Maui.Controls.dll!Microsoft.Maui.Controls.VisualElement.ArrangeOverride(Microsoft.Maui.Graphics.Rect bounds) Line 2005	C#
 	Microsoft.Maui.Controls.dll!Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IView.Arrange(Microsoft.Maui.Graphics.Rect bounds) Line 1993	C#
 	Microsoft.Maui.dll!Microsoft.Maui.Layouts.GridLayoutManager.ArrangeChildren(Microsoft.Maui.Graphics.Rect bounds) Line 46	C#
 	Microsoft.Maui.Controls.dll!Microsoft.Maui.Controls.Layout.CrossPlatformArrange(Microsoft.Maui.Graphics.Rect bounds) Line 384	C#
 	Microsoft.Maui.dll!Microsoft.Maui.Platform.MauiView.CrossPlatformArrange(CoreGraphics.CGRect bounds) Line 532	C#
 	Microsoft.Maui.dll!Microsoft.Maui.Platform.MauiView.LayoutSubviews() Line 622	C#
 	Microsoft.iOS.dll!ObjCRuntime.Messaging.void_objc_msgSend_bool(nint receiver, nint selector, byte arg1)	Unknown
 	Microsoft.iOS.dll!ObjCRuntime.Messaging.void_objc_msgSend_bool(nint receiver, nint selector, byte arg1)	Unknown
 	Microsoft.iOS.dll!UIKit.UIApplication.StatusBarHidden.set(bool value)	Unknown
 	CustomApp.Maui.iOS.dll!CustomApp.Maui.iOS.Delegates.AppDelegate.FinishedLaunching(UIKit.UIApplication uiApplication, Foundation.NSDictionary launchOptions) Line 264	C#
 	Microsoft.iOS.dll!UIKit.UIApplication.xamarin_UIApplicationMain(int argc, nint argv, nint principalClassName, nint delegateClassName, nint* gchandle)	Unknown
 	Microsoft.iOS.dll!UIKit.UIApplication.UIApplicationMain(int argc, string[] argv, nint principalClassName, nint delegateClassName)	Unknown
 	Microsoft.iOS.dll!UIKit.UIApplication.Main(string[] args, System.Type principalClass, System.Type delegateClass)	Unknown