Fix IsDomainName
Fix IsDomainName

Make \.. legal (as it should be) and don't allocate a new var byte c
and every loop.

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