fix up strtoul_ui error handling

fix up strtoul_ui error handling

Two scanf() calls were converted to strtoul_ui() but the return
values were not updated to match.  scanf() returns the number of
matched "values" which for this usage is 1 on success.  strtoul_ui()
return 0 on success.  Update these call sites to match.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>