Keep valid reference to WidgetManagerDelegate in ContextMenuWidget lambdas (#2704)

Fixes #2703

Author: bluemarvin

app/src/common/shared/org/mozilla/vrbrowser/ui/widgets/menus/ContextMenuWidget.java

@@ -77,17 +77,18 @@ public void setDismissCallback(Runnable aCallback) {
     public void setContextElement(GeckoSession.ContentDelegate.ContextElement aContextElement) {
         mItems = new ArrayList<>();
         mItems.add(new MenuWidget.MenuItem(aContextElement.linkUri, 0, null));
+        final WidgetManagerDelegate widgetManager = mWidgetManager;
         if (mWidgetManager.canOpenNewWindow()) {
             mItems.add(new MenuWidget.MenuItem(getContext().getString(R.string.context_menu_open_new_window_1), 0, () -> {
                 if (!StringUtils.isEmpty(aContextElement.linkUri)) {
-                    mWidgetManager.openNewWindow(aContextElement.linkUri);
+                    widgetManager.openNewWindow(aContextElement.linkUri);
                 }
                 onDismiss();
             }));
         }
         mItems.add(new MenuWidget.MenuItem(getContext().getString(R.string.context_menu_open_new_tab_1), 0, () -> {
             if (!StringUtils.isEmpty(aContextElement.linkUri)) {
-                mWidgetManager.openNewTab(aContextElement.linkUri);
+                widgetManager.openNewTab(aContextElement.linkUri);
                 GleanMetricsService.Tabs.openedCounter(GleanMetricsService.Tabs.TabSource.CONTEXT_MENU);
             }
             onDismiss();