Fix mosquitto_sub %j or %J not working on Windows.

Closes #1674. Thanks to amigian74.

ChangeLog.txt

@@ -12,6 +12,9 @@ Client library:
 - Don't treat an unexpected PUBACK, PUBREL, or PUBCOMP as a fatal error.
   Issue #1629.
 
+Clients:
+- Fix mosquitto_sub %j or %J not working on Windows. Closes #1674.
+
 Build:
 - Various fixes for building with <C99 support. Closes #1622.
 - Fix use of sed on BSD. Closes #1614.

client/sub_client_output.c

@@ -114,7 +114,7 @@ static void json_print(const struct mosquitto_message *message, const struct tm
 {
 	char buf[100];
 
-	strftime(buf, 100, "%s", ti);
+	snprintf(buf, 100, "%ld", time(NULL));
 	printf("{\"tst\":%s,\"topic\":\"%s\",\"qos\":%d,\"retain\":%d,\"payloadlen\":%d,", buf, message->topic, message->qos, message->retain, message->payloadlen);
 	if(message->qos > 0){
 		printf("\"mid\":%d,", message->mid);