Fix can't get dns server on macos and ios (#401)

If DNS configuration didn't include search domains on MacOS (or iOS) it would throw an error instead of ignoring.

Fix By: @halx99

src/lib/ares_init.c

@@ -1665,7 +1665,7 @@ static int init_by_resolv_conf(ares_channel channel)
       int entries = 0;
       while ((entries < MAXDNSRCH) && res.dnsrch[entries])
         entries++;
-
+      if(entries) {
         channel->domains = ares_malloc(entries * sizeof(char *));
         if (!channel->domains) {
           status = ARES_ENOMEM;
@@ -1679,6 +1679,7 @@ static int init_by_resolv_conf(ares_channel channel)
           }
         }
       }
+    }
     if (channel->ndots == -1)
       channel->ndots = res.ndots;
     if (channel->tries == -1)