Fix display of idle processes, which had been broken since rev. 1.56 of
machine.c. The traditional condition was (pctcpu > 0 || SRUN), but the
negation of the condition logic (from select to skip) made this come
out as (pctcpu > 0 && SRUN), leading to a very erratic display, except
for purely CPU bound processes.

This has been discussed in the mail lists some time ago and I have used
top with this patch on my systems for more than a year without problems
(just forgot to commit it earlier, since my systems were all fixed ...).