#90 [PHP]Modify return value of cubrid_num_fields

[Jira Trac]

[mysql_num_fields|http://www.php.net/manual/en/function.mysql-num-fields.php] will return *FALSE* on failure. However, [cubrid_num_fields|http://www.php.net/manual/en/function.cubrid-num-fields.php] will return -1. We need to make it completely compatible.