Update DB Script for loan counter changes

In the previous db version of db script file,

ALTER TABLE `m_client_loan_counter`
  ADD COLUMN `group_id` BIGINT(20) NOT NULL AFTER `client_id`,
  ADD CONSTRAINT `FK_m_group_loan_counter` FOREIGN KEY (`group_id`) REFERENCES `m_group` (`id`); 

The above script causes the build failure if we have any data in m_client_loan_counter table, 
because of the "NOT NULL" constraint.