Add check for search_result_ pointer to prevent browser crash

Fixes browser crash after search result answer card search

Bug: 910388
Change-Id: I7ab881d2cf4da2920439be73da2977a7c436b6af
Reviewed-on: https://chromium-review.googlesource.com/c/1356715Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Weidong Guo <weidongg@chromium.org>
Commit-Queue: Matthew Mourgos <mmourgos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612954}

ash/app_list/views/search_result_answer_card_view.cc

@@ -276,7 +276,8 @@ class SearchResultAnswerCardView::SearchAnswerContainerView
       AddChildView(content_view);
       ExcludeCardFromEventHandling(contents_->GetView()->native_view());
 
-      if (search_result_->equivalent_result_id().has_value()) {
+      if (search_result_ &&
+          search_result_->equivalent_result_id().has_value()) {
         view_delegate_->GetSearchModel()->DeleteResultById(
             search_result_->equivalent_result_id().value());
       }