go-ntlmssp NTLM challenges can panic on malformed payloads

go-ntlmssp is a Go package that provides NTLM/Negotiate authentication over HTTP. Prior to version 0.1.1, a malicious NTLM challenge message can causes an slice out of bounds panic, which can crash any Go process using `ntlmssp.Negotiator` as an HTTP transport. Version 0.1.1 patches the issue.