fix access array offset which doesn't exist and check if returned value is null

This check is used since default array is empty if user folder was not found

Signed-off-by: Jan Messer <jan@mtec-studios.ch>

Author: Messj1

lib/FilesHooks.php

@@ -396,7 +396,10 @@ protected function fileMoving($oldPath, $newPath) {
 		}
 		$accessList = $this->getUserPathsFromPath($parentPath, $parentOwner);
 		$affectedUsers = $accessList['users'];
-		$oldUsers = $this->oldAccessList['users'];
+        if(!isset($this->oldAccessList['users'])) return;
+        $oldUsers = $this->oldAccessList['users'];
+
+        if($oldUsers==null) return;
 
 		// file can be shared using GroupFolders, including ACL check
 		if ($this->config->getSystemValueBool('activity_use_cached_mountpoints', false)) {