Fix IPv6 lookups to return empty response

The logic here wasn't quite right and was returning an A record in
response to an AAAA lookup.

This returns nothing, which is better, but not quite enough: this gives
empty responses, which produces warnings in host/dig.

llarp/handlers/tun.cpp

@@ -509,12 +509,14 @@ namespace llarp
       else if(msg.questions[0].qtype == dns::qTypeA
               || msg.questions[0].qtype == dns::qTypeAAAA)
       {
-        const bool isV6 =
-            msg.questions[0].qtype == dns::qTypeAAAA && SupportsV6();
+        const bool isV6 = msg.questions[0].qtype == dns::qTypeAAAA;
         const bool isV4 = msg.questions[0].qtype == dns::qTypeA;
         llarp::service::Address addr;
+        if(isV6 && !SupportsV6())
+        { // empty reply but not a NXDOMAIN so that client can retry IPv4
+        }
         // on MacOS this is a typeA query
-        if(is_random_snode(msg))
+        else if(is_random_snode(msg))
         {
           RouterID random;
           if(Router()->GetRandomGoodRouter(random))