[stable22] Check for disk_free_space

Backport of https://github.com/nextcloud/server/pull/29758

lib/private/Files/Storage/Local.php

@@ -378,7 +378,7 @@ class Local extends \OC\Files\Storage\Common {
 			// disk_free_space doesn't work on files
 			$sourcePath = dirname($sourcePath);
 		}
-		$space = @disk_free_space($sourcePath);
+		$space = function_exists('disk_free_space') ? disk_free_space($sourcePath) : false;
 		if ($space === false || is_null($space)) {
 			return \OCP\Files\FileInfo::SPACE_UNKNOWN;
 		}