Skip if $this->active is empty.

Somehow, I still see error that $this->active is NULL, from line 195.

src/Plugin/ConfigFilter/ConfigSplitIgnoreFilter.php

@@ -189,7 +189,7 @@ class ConfigSplitIgnoreFilter extends IgnoreFilter {
       }
     }
 
-    if (!empty($this->getFilteredStorage()->getCollectionName())) {
+    if (!empty($this->getFilteredStorage()->getCollectionName()) && !empty($this->active)) {
       // In collections, treat config as existing
       // if it is ignored and exists in the active storage.
       $active_names = $this->active->listAll($prefix);