* LDAP/Addressbook: fix region contains for given country invalid value gives an LDAP error on update

cause by trying to write NULL, which is not allowed, unsetting the attribute the proper way now

api/src/Contacts/Ldap.php

@@ -596,7 +596,7 @@ class Ldap
 					$ldapContact[$ldapFieldName] = $ldapFieldName == 'jpegphoto' ? $data[$egwFieldName] :
 						Api\Translation::convert($data[$egwFieldName], $this->charset,'utf-8');
 				}
-				elseif($isUpdate && isset($data[$egwFieldName]))
+				elseif($isUpdate && array_key_exists($egwFieldName, $data))
 				{
 					$ldapContact[$ldapFieldName] = array();
 				}