packStructValue: fix a overflow in NSEC packing
packStructValue: fix a overflow in NSEC packing

modulexcite/dns,ErikDubbelboer/dns,letsencrypt/dns,skyportsystems/dns,josephyzhou/dns,miekg/dns,michaelharo/dns,curtiszimmerman/dns,bboreham/dns,skynet/dns,asergeyev/dns,tsenart/dns,jmhodges/dns,hugozhu/dns,tempbottle/dns,Psiphon-Inc/dns,ezoic/dns,bragr/dns,cloudflare/dns,janstk/dns