max_getkey_inactivity set to 0 is not "Unlimited"

Setting SCFG:System->Advanced->Maximum User Inactivity to 0 (Unlimited) actually just enables a very short user inactivity.

A quick glance at the SBBS code seems to confirm this. Probably best to just fix SCFG to not report this value as "Unlimited".

Reported on DOVE-Net by Scott Duensing