ps: swat insidious bug with the %cpu' format specifier

ps: swat insidious bug with the %cpu' format specifier

Whoa, my head really hurts but this commit should help
with a speedy recovery hopefully, after it is applied.

If the '%cpu' field is used as a format specifier with
that 'o' option, you will encounter a SIGSEGV if there
is also an invalid argument on that same command line.

For example, try 'ps/pscommand -o %cpu,x' with newlib.
With any format specifier other than the '%cpu', there
is an error message, as would happen with '-o pcpu,x'.

For a 3.3.17 version of ps, there's no abend. Instead,
the program will just display a bunch of gobbledygook.
This boo-boo was found to exist as far back as v3.3.0.

[ ok, i am starting to feel very much better already ]

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