ResolveAsync does not iterate through all servers

[djugessur]

Repro code below, check the comment for where it throws vs it doesn't.

List<IPAddress> lDnsServers = new List<IPAddress>();
lDnsServers.Add(IPAddress.Parse("1.4.5.6")); // non existent
lDnsServers.Add(IPAddress.Parse("8.8.8.8"));

DnsClient lClient = new DnsClient(lDnsServers, 5000);
lClient.IsTcpEnabled = true;
var resolver = new DnsStubResolver(lClient);
var records1 = resolver.Resolve<MxRecord>(lDomain, RecordType.Mx); // this will NOT throw and get the result from 8.8.8.8
var records2 = await resolver.ResolveAsync<MxRecord>(lDomain, RecordType.Mx).ConfigureAwait(false); // this will throw on the non existent server and never query 8.8.8.8

[henning-krause]

See Netatwork-de@8bc9245 for a fix.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.