The loops in update_one can be increased in two different ways: step
by one for files and by <n> for directories. "for" loop is not
suitable for this as it always steps by one and special handling is
required for directories. Replace them with "while" loops for clarity.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>