While generating the Income Tax Computation report, if an employee does not have pre-existing salary slips, the system looks for salary structure assignments on or before the selected Payroll Period start date. But an employee might not have a salary structure assignment till from when they joined, which could be after the aforementioned Payroll Period start date. In such a case, the system throws an error.

This PR fixes this by looking for assignments on or before the date of joining for such employees.