setCategories will remove all other tags of a customer :-(

[rycks]

Surprise today, an old customer with 20 tags make a new order online ... and "boum" now he has only one tag !

I don't have the time to make a PR, here is the problem (register_instance.php)

	if (! empty($conf->global->SELLYOURSAAS_DEFAULT_CUSTOMER_CATEG)) {
		dol_syslog("register_instance.php We will set customer into the categroy");

		$result = $tmpthirdparty->setCategories(array($conf->global->SELLYOURSAAS_DEFAULT_CUSTOMER_CATEG => $conf->global->SELLYOURSAAS_DEFAULT_CUSTOMER_CATEG), 'customer');
		if ($result < 0) {