top: avoid a 'nan' when the delay interval is very low

The granularity of /proc/uptime is fixed at hundredths
of a second. And, since we can cycle faster than that,
we are exposed to 'nan' when calculating elapsed time.

This commit will protect us from that outcome when the
delay interval has been set to an extremely low value.

Signed-off-by: Jim Warner <james.warner@comcast.net>

top/top.c

@@ -2525,6 +2525,7 @@ static void procs_hlp (proc_t *this) {
 
       uptime(&uptime_cur, NULL);
       et = uptime_cur - uptime_sav;
+      if (et < 0.01) et = 0.005;
       uptime_sav = uptime_cur;
 
       // if in Solaris mode, adjust our scaling for all cpus