Avoiding voice search crash if none of search providers returned anything.

It's highly unlikely that this can happen, but just in case.

The voice search popup will keep staying with no other way to dismiss it except reopening the launcher, but I don't think we should take too much care of this edge case beyond simply not breaking.

Bug=712331

Review-Url: https://codereview.chromium.org/2848493004
Cr-Commit-Position: refs/heads/master@{#468068}

ui/app_list/views/search_result_list_view.cc

@@ -223,7 +223,10 @@ void SearchResultListView::VisibilityChanged(views::View* starting_from,
 
 void SearchResultListView::AnimationEnded(const gfx::Animation* animation) {
   DCHECK_EQ(auto_launch_animation_.get(), animation);
-  view_delegate_->OpenSearchResult(results()->GetItemAt(0), true, ui::EF_NONE);
+  if (results()->item_count() > 0) {
+    view_delegate_->OpenSearchResult(results()->GetItemAt(0), true,
+                                     ui::EF_NONE);
+  }
 
   // The auto-launch has to be canceled explicitly. Think that one of searcher
   // is extremely slow. Sometimes the events would happen in the following