app_service: Fix possible crash on open native settings.

BUG=924872
TEST=None

Change-Id: I5df8485c1a978d8f7ec29516d2900445bf225244
Reviewed-on: https://chromium-review.googlesource.com/c/1435682
Commit-Queue: Yury Khmel <khmel@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626218}

chrome/browser/apps/app_service/arc_apps.cc

@@ -231,6 +231,11 @@ void ArcApps::Uninstall(const std::string& app_id) {
 void ArcApps::OpenNativeSettings(const std::string& app_id) {
   const std::unique_ptr<ArcAppListPrefs::AppInfo> app_info =
       prefs_->GetApp(app_id);
+  if (!app_info) {
+    LOG(ERROR) << "Cannot open native settings for " << app_id
+               << ". App is not found.";
+    return;
+  }
   arc::ShowPackageInfo(app_info->package_name,
                        arc::mojom::ShowPackageInfoPage::MAIN,
                        display::Screen::GetScreen()->GetPrimaryDisplay().id());