gc: fix cast in compare_tasks_by_selection()
compare_tasks_by_selection() is used with QSORT and gets passed pointers
to the elements of "static struct maintenance_task tasks[]". It casts
the *addresses* of these passed pointers to element pointers, though,
and thus effectively compares some unrelated values from the stack. Fix
the casts to actually compare array elements.
Detected by USan (make SANITIZE=undefined test).
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>