[iOS] Prevent crash when a leaked cell has MenuItem with bindings (#3288)

* Prevent crash when a leaked cell in ListView with Recycle mode has MenuItem with bindings and framework like Xamarin.Forms sets BindingContext to null after leaving the page

* Made SetupSelection static

Xamarin.Forms.Platform.iOS/ContextActionCell.cs

@@ -630,8 +630,11 @@ namespace Xamarin.Forms.Platform.iOS
 			return null;
 		}
 
-		void SetupSelection(UITableView table)
+		static void SetupSelection(UITableView table)
 		{
+			if (table.GestureRecognizers == null)
+				return;
+
 			for (var i = 0; i < table.GestureRecognizers.Length; i++)
 			{
 				var r = table.GestureRecognizers[i] as SelectGestureRecognizer;
@@ -639,7 +642,7 @@ namespace Xamarin.Forms.Platform.iOS
 					return;
 			}
 
-			_tableView.AddGestureRecognizer(new SelectGestureRecognizer());
+			table.AddGestureRecognizer(new SelectGestureRecognizer());
 		}
 
 		class SelectGestureRecognizer : UITapGestureRecognizer