d9bd4cbb9cc (config: flip return value of store_write_*()) made
write_section() follow the convention of write(2) to return -1 on error
and the number of written bytes on success.
3b48045c6c7 (Merge branch
'sd/branch-copy') changed it back to returning 0 on error and 1 on
success, but left its callers still checking for negative values.
Let write_section() follow the convention of write(2) again to meet the
expectations of its callers.
Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>