This ensures that the cookie is preserved when the server sets an additional cookie.

ntdll: Fix read_directory_getattrlist() to get the name of a symlink rather than its target, but still detect if the symlink is broken.

ntdll: If read_directory_getattrlist() finds that the file doesn't exist, return successful "no file" result to stop search.

The docs for getattrlist() say that ATTR_CMN_NAME can return up to NAME_MAX + 1
Unicode characters (code points) encoded in UTF-8, which means it can be up to
NAME_MAX * 3 + 1 bytes.

Based on a patch by Qian Hong.