bug#13553: 24.3.50; incorrect usage of IS_DIRECTORY_SEP

[Stefan Monnier]

> It is because IS_DIRECTORY_SEP is wrongly used.
> IS_DIRECTORY_SEP only works when its argument is surely on a start
> byte of dbcs characters.

If the file name is properly decoded (i.e. in its multibyte form), there
can't be a 0x5c byte other than at the beginning of a char.

So this bug can only happens if you pass a unibyte filename.  IOW the
bug is probably in the caller rather than in the file-attributes function.

Please show us the actual situation where this happens, since file names
are normally always multibyte.


        Stefan