nghttpx: Just return DNS_STATUS_ERROR

At the moment, we use both resolvers, and if either one is not
DNS_STATUS_IDLE, the other one is also not DNS_STATUS_IDLE.  This may
change if we are going to configure DNS so that either A or AAAA
lookup is done.  In that case, it is better to just return
DNS_STATUS_ERROR in the diff.  This is because the calling side does
not expect DNS_STATUS_IDLE in that case.

src/shrpx_dual_dns_resolver.cc

@@ -78,7 +78,7 @@ int DualDNSResolver::get_status(Address *result) const {
   if (rv4 == DNS_STATUS_RUNNING || rv6 == DNS_STATUS_RUNNING) {
     return DNS_STATUS_RUNNING;
   }
-  if (rv4 == DNS_STATUS_ERROR && rv6 == DNS_STATUS_ERROR) {
+  if (rv4 == DNS_STATUS_ERROR || rv6 == DNS_STATUS_ERROR) {
     return DNS_STATUS_ERROR;
   }
   return DNS_STATUS_IDLE;