[iOS] System.NullReferenceException at NavigationRenderer.SetStatusBarStyle() (#29564)

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### Issues Fixed

Fixes #29535

Author: kubaflo

src/Compatibility/Core/src/iOS/Renderers/NavigationRenderer.cs

@@ -762,6 +762,11 @@ void UpdateBarTextColor()
 
 		void SetStatusBarStyle()
 		{
+			if (NavPage is null)
+			{
+				return;
+			}
+
 			var barTextColor = NavPage.BarTextColor;
 			var statusBarColorMode = NavPage.OnThisPlatform().GetStatusBarTextColorMode();
 

src/Controls/src/Core/Compatibility/Handlers/NavigationPage/iOS/NavigationRenderer.cs

@@ -968,6 +968,11 @@ void UpdateBarTextColor()
 
 		void SetStatusBarStyle()
 		{
+			if (NavPage is null)
+			{
+				return;
+			}
+			
 			var barTextColor = NavPage.BarTextColor;
 			var statusBarColorMode = NavPage.OnThisPlatform().GetStatusBarTextColorMode();