chrt: do not try to interpret any other option as a PID either

chrt: do not try to interpret any other option as a PID either

When doing, for example, `chrt --pid --max`, it would report:

  chrt: invalid PID argument: '--max'

This mistakenly gave the impression that the PID argument has to follow
directly after the --pid option.

Avoid this by delaying the parsing of a PID until after all options have
been parsed.  Temporarily set 'ctl->pid' to zero to indicate that a PID
needs to be read.

After this change, `chrt --pid --max` will simply report the minimum and
maximum valid priorities.  And `chrt --pid -v`:

  chrt: too few arguments

Also, add a missing call of gettext() for the other error message.

CC: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Signed-off-by: Benno Schulenberg <bensberg@telfort.nl>