lib-lda: Cleanup error handling in LMTP client code.

If there are no successful recipients, we'll need to deinit the client.
But at that point we've already called all the callbacks, so the line
parameter to lmtp_client_fail_full() isn't actually used anywhere.
This was confusing static analyzer because global_fail_string was used
as parameter, which could have been NULL and wouldn't have been valid
for the callbacks.

src/lib-lda/lmtp-client.c

@@ -274,10 +274,14 @@ static int lmtp_client_send_data_cmd(struct lmtp_client *client)
 	if (client->rcpt_next_receive_idx < array_count(&client->recipients))
 		return 0;
 
-	if (client->global_fail_string != NULL || !client->rcpt_to_successes) {
+	if (client->global_fail_string != NULL) {
 		lmtp_client_fail_full(client, client->global_fail_string,
 				      client->global_remote_failure);
 		return -1;
+	} else if (!client->rcpt_to_successes) {
+		/* This error string shouldn't become visible anywhere */
+		lmtp_client_fail_full(client, "No valid recipients", FALSE);
+		return -1;
 	} else {
 		client->input_state++;
 		o_stream_nsend_str(client->output, "DATA\r\n");