fix buffer overrun in unpack()
fix buffer overrun in unpack()

bragr/dns,flebarbe/dns,bboreham/dns,michaelharo/dns,tsenart/dns,modulexcite/dns,Psiphon-Inc/dns,miekg/dns,skynet/dns,benbearchen/dns,ErikDubbelboer/dns,ezoic/dns,jdef/dns,cloudflare/dns,tempbottle/dns,letsencrypt/dns,skyportsystems/dns,ym/go-dns,josephyzhou/dns,Git-Host/dns,rolandshoemaker/dns,janstk/dns,jmhodges/dns,asergeyev/dns,curtiszimmerman/dns,hugozhu/dns