Fix crash in ReparentItemToAnotherFolder() on Windows app list.

ui/app_list/views/apps_grid_view.cc

Index: ui/app_list/views/apps_grid_view.cc
diff --git a/ui/app_list/views/apps_grid_view.cc b/ui/app_list/views/apps_grid_view.cc
index 5a620a6270152c26c6b3aaf8ed0ec9a953d12074..e30092b639fd06ffbd76d2fcc116f991b9e253b5 100644
--- a/ui/app_list/views/apps_grid_view.cc
+++ b/ui/app_list/views/apps_grid_view.cc
@@ -1671,6 +1671,11 @@ void AppsGridView::ReparentItemToAnotherFolder(views::View* item_view,
                                                const Index& target) {
   DCHECK(IsDraggingForReparentInRootLevelGridView());
 
+  AppListItemView* target_view =
+      static_cast<AppListItemView*>(GetViewAtSlotOnCurrentPage(target.slot));
+  if (!target_view)
+    return;
+
   // Make change to data model.
   item_list_->RemoveObserver(this);
 
@@ -1686,8 +1691,6 @@ void AppsGridView::ReparentItemToAnotherFolder(views::View* item_view,
   if (source_folder->ChildItemCount() == 1u)
     DeleteItemViewAtIndex(view_model_.GetIndexOfView(activated_item_view()));
 
-  AppListItemView* target_view =
-      static_cast<AppListItemView*>(GetViewAtSlotOnCurrentPage(target.slot));
   AppListItem* target_item = target_view->item();
 
   // Move item to the target folder.