resolved: fix ResolveService() hostname handling

Let's eat up special returns of dns_query_process_cname_many() when
storing hostname resolution results.

The rest of the code assumes only == 0 means success and != 0 means
error, but so far > 0 also could mean success, let's fix that.

Fixes: #21365 #21140

(This was originally broken in 1db8e6d1db)

src/resolve/resolved-bus.c

@@ -1005,6 +1005,7 @@ static void resolve_service_all_complete(DnsQuery *q) {
                                         goto finish;
                                 }
 
+                                assert(bad->auxiliary_result < 0);
                                 r = bad->auxiliary_result;
                                 goto finish;
                         }
@@ -1112,7 +1113,7 @@ static void resolve_service_hostname_complete(DnsQuery *q) {
                 return;
 
         /* This auxiliary lookup is finished or failed, let's see if all are finished now. */
-        q->auxiliary_result = r;
+        q->auxiliary_result = r < 0 ? r : 0;
         resolve_service_all_complete(q->auxiliary_for);
 }