DNS parsing can cause crash due to infinite recursion

[jmaygarden]

The name parsing uses a u16 offset and recurses without checking if the value is zero. That may cause an infinite loop that blows up the stack and crashes the process.

See tailhook/dns-parser@c840c17 for a fix.

[willstott101]

Thanks, I'll try and get this integrated this weekend. Medium-term I think it would be best for this library to switch to a maintained external DNS serialization library though.