[CBRD-25319] fix FQDN stytle hostname error in use_user_hosts

[kisoo-han]

http://jira.cubrid.org/browse/CBRD-25319

Description

• Fix usage of FQDN (like cubrid.co.kr) with 'use_user_hosts' service

Remarks

• To verify the valid hostname, following codes were used:

321  else if (is_valid_ip (temp_token) == true)
322    {
323      continue;
324    }
325  else if (is_valid_hostname (temp_token, str_len) == false)
326   {
327     continue;
328   }

• When line # 321 is called, the temp_token value can be changed to NULL or another value by strtok_r (), which is what we didn't expect.
• In this case, is_valid_hostname () could fails at line#325, with subject hostname to NULL
  • maybe it have been called in is_valid_hostname (NULL, 7) style, not is_valid_hostname ("dev2.com", 7)