top: Off-by-one error in PID length

When kernel.pid_max is set to 100000, then top reserves a field with 6 characters width for the PID.

However, according to section "pid_max" in Linux admin-guide/sysctl/kernel.rst:

PID allocation wrap value. When the kernel's next PID value reaches this value, it wraps back to a minimum PID value. PIDs of value "pid_max" or larger are not allocated.

That is, for pid_max = 100000 the maximum possible PID value is 99999 and the field should be only 5 characters wide.