lib-http: client: Fixed race condition between DNS refresh lookup and…

… a soft connection timeout.

The refreshing DNS lookup cleared all the IPs, but the soft connection timeout (and maybe other code) still relied on them.
Adding tests everywhere for host->ips_count == 0 is annoying, so I changed the DNS lookup code such that the stale IPs remain present while the DNS lookup is being performed.
The pending lookup prevents new connections through http_client_host_refresh(), so this will not create potentially useless connections.

src/lib-http/http-client-host.c

@@ -108,8 +108,6 @@ static void http_client_host_lookup
 	i_assert(!host->explicit_ip);
 	i_assert(host->dns_lookup == NULL);
 
-	host->ips_count = 0;
-
 	if (client->set.dns_client != NULL) {
 		http_client_host_debug(host,
 			"Performing asynchronous DNS lookup");
@@ -147,9 +145,7 @@ static void http_client_host_lookup
 		host->ips_count = ips_count;
 		host->ips = i_new(struct ip_addr, ips_count);
 		memcpy(host->ips, ips, ips_count * sizeof(*ips));
-	}
 
-	if (host->ips_count > 0) {
 		host->ips_timeout = ioloop_timeval;
 		timeval_add_msecs(&host->ips_timeout, client->set.dns_ttl_msecs);
 	}