fix: Throw instead of yielding nothing when listing local directories

Signed-off-by: Julius Härtl <jus@bitgrid.net>
Signed-off-by: Max <max@nextcloud.com>

lib/private/Files/Storage/Common.php

@@ -877,6 +877,11 @@ public function writeStream(string $path, $stream, int $size = null): int {
 
 	public function getDirectoryContent($directory): \Traversable {
 		$dh = $this->opendir($directory);
+
+		if ($dh === false) {
+			throw new StorageNotAvailableException('Directory listing failed');
+		}
+
 		if (is_resource($dh)) {
 			$basePath = rtrim($directory, '/');
 			while (($file = readdir($dh)) !== false) {