cros: Fix launcher not shown while logging in during tablet mode

We were dismissing the launcher when logging in via tablet mode.

Check for tablet mode before dismissing.

Bug: 988378
Change-Id: Ie956dabd899be4dc849e2eed845a02dbd4d0e7b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1730765Reviewed-by: Matthew Mourgos <mmourgos@chromium.org>
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683292}

ash/app_list/app_list_controller_impl.cc

@@ -593,6 +593,7 @@ ash::AppListViewState AppListControllerImpl::GetAppListViewState() {
 }
 
 void AppListControllerImpl::OnShelfAlignmentChanged(aura::Window* root_window) {
+  if (!IsHomeScreenAvailable())
     DismissAppList();
 }