nonappcompat check if MDP Icon is null (#7162)

fixes #6958

Xamarin.Forms.Platform.Android/Platform.cs

@@ -574,7 +574,7 @@ namespace Xamarin.Forms.Platform.Android
 				ClearMasterDetailToggle();
 				return;
 			}
-			if (!CurrentMasterDetailPage.ShouldShowToolbarButton() || CurrentMasterDetailPage.Master.IconImageSource.IsEmpty ||
+			if (!CurrentMasterDetailPage.ShouldShowToolbarButton() || (CurrentMasterDetailPage.Master.IconImageSource?.IsEmpty ?? true) ||
 				(MasterDetailPageController.ShouldShowSplitMode && CurrentMasterDetailPage.IsPresented))
 			{
 				//clear out existing icon;