num_attr is incremented iff parse_attr() returns non-NULL. So do the
counting in parse_attr_line() instead of within parse_attr(). This
allows an integer rather than a pointer to an integer to be passed to
parse_attr().
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>