net/cjdns: fix build on powerpc64*

On powerpc64 and powerpc64le systems, os.cpus(), gets defined to []:

cpus = os.cpus()

It has type object:

typeof cpus

'object'

This causes jobs to be 0:

Math.floor((typeof cpus === 'undefined' ? 1 : cpus.length) * 1.25);

0

Change it so that instead of comparing type to undefined, we compare to 0:

Math.floor((os.cpus() == 0 ? 1 : cpus.length) * 1.25);

1