fix(node): non-existing folder is not searchable

the previosuly introduced searchBySystemTag was not overwritten in
NonExistingFolder and could run the inherited method.

Signed-off-by: Arthur Schiwon <blizzz@arthur-schiwon.de>

lib/private/Files/Node/NonExistingFolder.php

@@ -154,6 +154,10 @@ public function searchByTag($tag, $userId) {
 		throw new NotFoundException();
 	}
 
+	public function searchBySystemTag(string $tagName, string $userId, int $limit = 0, int $offset = 0): array {
+		throw new NotFoundException();
+	}
+
 	public function getById($id) {
 		throw new NotFoundException();
 	}