Add Draft or Archived to title assume content moderation module is installed

[andybroomfield]

When using a Localgov_base derived theme, switching on the option to show draft / archive in front of the page title leads to a WSOD if the content moderation (and I assume localgov_workflow) is not installed.

Steps to replicate

1. Go to /admin/appearance/settings/localgov_scarfolk (or settings page for your localgov_base derived theme)
2. Select Add "Draft" to title of draft unpublished content.
3. Optionally also select Add "Archived" to title of archived content.
4. Visit an unpublished page that does not have content moderation or a workflow set up.

Expected result

Page should show, if it is unpublished I would expect to see Draft in front of the title.

Actual result

WSOD with error:

InvalidArgumentException: Field moderation_state is unknown. in Drupal\Core\Entity\ContentEntityBase->getTranslatedField() (line 616 of core/lib/Drupal/Core/Entity/ContentEntityBase.php).
Drupal\Core\Entity\ContentEntityBase->get('moderation_state') (Line: 323)
localgov_base_preprocess_node(Array, 'node', Array)
call_user_func_array('localgov_base_preprocess_node', Array) (Line: 261)
Drupal\Core\Theme\ThemeManager->render('node', Array) (Line: 490)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 248)
Drupal\Core\Render\Renderer->render(Array, ) (Line: 238)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent{closure}() (Line: 637)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 231)
Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 128)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object)
call_user_func(Array, Object, 'kernel.view', Object) (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.view') (Line: 186)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 53)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle(Object, 1, 1) (Line: 116)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 90)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 36)
Drupal\Core\StackMiddleware\AjaxPageState->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object, 1, 1) (Line: 741)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

[andybroomfield]

It's this part of localgov_base

localgov_base/localgov_base.theme

Lines 320 to 336 in 36658bd

	if ($node_status === FALSE) {
	if (theme_get_setting('localgov_base_add_draft_note_to_unpublished_content') === TRUE) {
	$state = $variables['node']->get('moderation_state')->getString();
	if ($state == 'draft') {
	$variables['label'] = t('[Draft]') . " " . $variables['node']->label();
	}
	}
	}
	// We have a theme setting to prepend 'archived' to the title of
	// archived content, but we don't mind whether it is published or not.
	// An archived state does not have to always be unpubilshed.
	if (theme_get_setting('localgov_base_add_archived_note_to_archived_content') === TRUE) {
	$state = $variables['node']->get('moderation_state')->getString();
	if ($state == 'archived') {
	$variables['label'] = t('[Archived]') . " " . $variables['node']->label();
	}
	}

Fix should be same as #854. Use a Null safe operator to get the moderation state, defaulting to draft if no moderation state found.