Craig Small bed6074531 ps: Stop crash if using test fields
I'm not sure if anyone actually uses these things, but if you
selected test fields on the command line ps would crash.

$ ps/pscommand -o _left
Signal 11 (SEGV) caught by pscommand (3.3.11.877-0488).
/home/csmall/Projects/procps/procps/ps/.libs/pscommand:ps/display.c:66: please report this bug
Segmentation fault

Anyway, it doesn't now:
$ ps/pscommand -o pid,_left,_left2,_right,_unlimited 1
    PID LLLLLLLL L2L2L2L2 RRRRRRRRRRR U
      1 tty7     3270/tty4      59:59 [123456789-12345] <defunct>
2020-12-22 17:50:17 +11:00
..
2012-03-04 08:04:24 +11:00
2016-04-16 17:03:57 +10:00
2020-12-22 17:50:17 +11:00
2020-12-22 11:40:23 +11:00
2002-02-01 22:47:29 +00:00
2020-09-24 22:19:11 +10:00