Deleting cluster used for Search API server backend causes fatal error

It appears that it is still possible to delete Elasticsearch clusters that are the backend for a Search API index in elasticsearch_connector-8.x-7.x-dev. However, it is not possible in the 8.0.x branch.

To reproduce it on 8.x-7.x...

1. Go to /admin/config/search/elasticsearch-connector/cluster/add and add a cluster. Check "Make this cluster default connection".
2. Go to /admin/config/search/elasticsearch-connector/cluster/add again, and add a second cluster. Do not check "Make this cluster default connection" this time.
3. Go to /admin/config/search/search-api/add-server and add a search server which points to the second cluster (the one that isn't the default).
4. Go to /admin/config/search/elasticsearch-connector and delete the second cluster.
5. Go to /admin/config/search/search-api: you get an error...
   

   Drupal\search_api\SearchApiException: Cannot load the Elasticsearch cluster for your index. in Drupal\elasticsearch_connector\Plugin\search_api\backend\SearchApiElasticsearchBackend->__construct() (line 205 of /var/www/html/src/Plugin/search_api/backend/SearchApiElasticsearchBackend.php).
   
   Drupal\elasticsearch_connector\Plugin\search_api\backend\SearchApiElasticsearchBackend::create() (Line: 21)
   Drupal\Core\Plugin\Factory\ContainerFactory->createInstance() (Line: 83)
   Drupal\Component\Plugin\PluginManagerBase->createInstance() (Line: 149)
   Drupal\search_api\Entity\Server->getBackend() (Line: 198)
   Drupal\search_api\Entity\Server->isAvailable() (Line: 209)
   Drupal\search_api\IndexListBuilder->buildRow() (Line: 241)
   Drupal\search_api\IndexListBuilder->render() (Line: 23)
   Drupal\Core\Entity\Controller\EntityListController->listing()
   call_user_func_array() (Line: 123)
   Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 638)
   Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 121)
   Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext() (Line: 97)
   Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 181)
   Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 76)
   Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 53)
   Drupal\Core\StackMiddleware\Session->handle() (Line: 48)
   Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 28)
   Drupal\Core\StackMiddleware\ContentLength->handle() (Line: 32)
   Drupal\big_pipe\StackMiddleware\ContentLength->handle() (Line: 106)
   Drupal\page_cache\StackMiddleware\PageCache->pass() (Line: 85)
   Drupal\page_cache\StackMiddleware\PageCache->handle() (Line: 48)
   Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
   Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 36)
   Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 51)
   Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 741)
   Drupal\Core\DrupalKernel->handle() (Line: 19)