Check for NPE when removing long press listener on buttons

android/app/src/main/java/com/reactnativenavigation/views/TitleBarButton.java

             @Override
             public void run() {
                 ActionMenuView actionMenuView = ViewUtils.findChildByClass(parent, ActionMenuView.class);
-                if (actionMenuView != null) {
+                if (actionMenuView != null && actionMenuView.getChildAt(index) != null) {
                     actionMenuView.getChildAt(index).setOnLongClickListener(null);
                 }
             }