Any officer, department, institution, committee, commission or other body of the state or any subdivision or municipality thereof, may pay in his or its discretion the whole or a part of the salaries or compensation of their employees or attaches during the time they are engaged in a branch of the military or naval service of the national government or of this state.
No greater portion of the salary or compensation of a commissioned officer as an employee of a department of the state or municipal government shall be paid to him under this section than will, when added to his salary as such commissioned officer, equal the amount paid to him by the state or municipal department before entering the military or naval service.