[iOS] Fix NRE when looking for internal buttons (#6170)

diff --git a/Xamarin.Forms.Platform.iOS/Extensions/UIViewExtensions.cs b/Xamarin.Forms.Platform.iOS/Extensions/UIViewExtensions.cs
index a641972..ba97c00 100644 (file)
--- a/Xamarin.Forms.Platform.iOS/Extensions/UIViewExtensions.cs
+++ b/Xamarin.Forms.Platform.iOS/Extensions/UIViewExtensions.cs
@@ -126,7 +126,7 @@ namespace Xamarin.Forms.Platform.MacOS
                                if (result != null)
                                        return result;
 
-                               for (var i = 0; i < descendantView.Subviews.Length; i++)
+                               for (var i = 0; i < descendantView.Subviews?.Length; i++)
                                        queue.Enqueue(descendantView.Subviews[i]);
                        }