resolved: cleanup use of ERRNO_IS_DISCONNECT()

Given that ERRNO_IS_DISCONNECT() also matches positive values,
make sure this macro is not called with arguments that do not have
errno semantics.

In this case the argument passed to ERRNO_IS_DISCONNECT() is the value
returned by dns_transaction_emit_tcp() and dns_transaction_emit_udp()
which are not expected to return any positive values, but let's be
consistent anyway and move the ERRNO_IS_DISCONNECT() invocation
to the branch where the return value is known to be negative.

src/resolve/resolved-dns-transaction.c

@@ -2079,7 +2079,7 @@ int dns_transaction_go(DnsTransaction *t) {
                 dns_transaction_complete(t, DNS_TRANSACTION_RR_TYPE_UNSUPPORTED);
                 return 0;
         }
-        if (t->scope->protocol == DNS_PROTOCOL_LLMNR && ERRNO_IS_DISCONNECT(r)) {
+        if (t->scope->protocol == DNS_PROTOCOL_LLMNR && r < 0 && ERRNO_IS_DISCONNECT(r)) {
                 /* On LLMNR, if we cannot connect to a host via TCP when doing reverse lookups. This means we cannot
                  * answer this request with this protocol. */
                 dns_transaction_complete(t, DNS_TRANSACTION_NOT_FOUND);