fsck: detect more in-tree d/f conflicts

fsck: detect more in-tree d/f conflicts

If the conflict candidate file name from the top of the stack is not a
prefix of the current candiate directory then we can discard it as no
matching directory can come up later.  But we are not done checking the
candidate directory -- the stack might still hold a matching file name,
so stay in the loop and check the next candidate file name.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>