iOS - Test and fix for VoiceOver crash on a ContentPage not having any Content defined (#6987) fixes #6926

* Added test case for showing crash for issue 6926.

* Potential fix for issue 6926. Prevents a null reference exception when a ContentPage has no Content.

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/GitHub6926.cs

@@ -0,0 +1,42 @@
+using System;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 6926, "[iOS] iOS - Using VoiceOver will crash when a ContentPage has no Content", PlatformAffected.iOS)]
+	public class GitHub6926 : TestContentPage
+	{
+		protected override void Init()
+		{
+			Content = new StackLayout
+			{
+				Children = {
+					new Label()
+					{
+						Text = "Enable VoiceOver and then click either:",
+						HorizontalTextAlignment = TextAlignment.Center,
+						VerticalTextAlignment = TextAlignment.Center,
+					},
+					new Button()
+					{
+						Text = "ContentPage without content (crash)",
+						Command = new Command(() =>
+						{
+							Navigation.PushAsync(new ContentPage());
+						})
+					},
+					new Button()
+					{
+						Text = "ContentPage with content (no crash)",
+						Command = new Command(() =>
+						{
+							Navigation.PushAsync(new ContentPage() { Content = new StackLayout() });
+						})
+					}
+				},
+			};
+		}
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -979,6 +979,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue3548.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue6472.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue6614.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)GitHub6926.cs" />
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Bugzilla22229.xaml">

Xamarin.Forms.Platform.iOS/Renderers/PageContainer.cs

@@ -62,6 +62,9 @@ namespace Xamarin.Forms.Platform.iOS
 		[Export("accessibilityElementCount")]
 		nint AccessibilityElementCount()
 		{
+			if (AccessibilityElements == null)
+				return 0;
+
 			// Note: this will only be called when VoiceOver is enabled
 			return AccessibilityElements.Count;
 		}