Don't ignore "permission denied" errors when enabling chroot

Don't ignore "permission denied" errors when enabling chroot

Up to now, ngIRCd silently ignored permission denied errors when trying
to enable a chroot setup: only the "not running chrooted" message became
logged later on.

This patch lets ngIRCd exit with a fatal error when the chroot can't
be enabled on startup -- this is the much safer bevahiour!