top(1): fixed the empty output problem in non-interactive mode (-n, -b) regressed in r336028

[daichi]

Summary

top(1): fixed the empty output problem in non-interactive mode (-n, -b) regressed in r336028

See:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=229842

Test Plan

original top:

# top -n -o res
last pid:  1497;  load averages:  0.33,  0.42,  0.40  up 0+00:56:42    20:14:54
29 processes:  1 running, 28 sleeping
CPU:  0.6% user,  0.0% nice,  0.5% system,  0.1% interrupt, 98.8% idle
Mem: 25M Active, 233M Inact, 2T Wired, 200M Buf, 1G Free
Swap: 2G Total, 2G Free





















#

patched top:

# ./top -n -o res
last pid:  1718;  load averages:  0.55,  0.39,  0.35  up 0+01:07:54    20:26:06
28 processes:  1 running, 27 sleeping
CPU:  0.6% user,  0.0% nice,  0.4% system,  0.1% interrupt, 98.9% idle
Mem: 19M Active, 243M Inact, 1963G Wired, 200M Buf, 1445M Free
Swap: 1638M Total, 1638M Free

  PID USERNAME    THR PRI NICE   SIZE    RES STATE    C   TIME    WCPU COMMAND
  762 daichi        1  20    0    18M  8080K select   0   0:00   0.00% sshd
  732 daichi        1  20    0    19M  8072K select   1   0:01   0.00% sshd
 1185 daichi        1  20    0    18M  8072K select   0   0:00   0.00% sshd
 1182 root          1  22    0    18M  8056K select   0   0:00   0.00% sshd
  759 root          1  23    0    18M  8056K select   0   0:00   0.00% sshd
  729 root          1  24    0    18M  8020K select   0   0:00   0.00% sshd
  630 root          1  20    0    18M  7108K select   1   0:00   0.00% sshd
  633 root          1  20    0    16M  6128K select   0   0:00   0.00% sendmail
  636 smmsp         1  20    0    15M  6040K pause    0   0:00   0.00% sendmail
  371 root          1  20    0    14M  5124K select   1   0:00   0.00% devd
  750 root          1  20    0    13M  4460K ttyin    1   0:00   0.00% csh
  766 root          1  20    0    13M  4452K pause    0   0:00   0.00% csh
 1189 root          1  52    0    13M  4452K ttyin    1   0:00   0.00% csh
  687 root          1  41    0    13M  4396K ttyin    0   0:00   0.00% csh
 1718 root          1  20    0    12M  3272K CPU1     1   0:00   0.00% top
  749 daichi        1  25    0    12M  3256K wait     0   0:00   0.00% su
 1188 daichi        1  27    0    12M  3256K wait     1   0:00   0.00% su
  765 daichi        1  26    0    12M  3256K wait     1   0:00   0.00% su

#

[eadler]

LGTM for now. There might be a way to query the terminal in some cases, but this is no worse than before.