If click button ‘Update’ in maintenance period form, then value of start date will be changed

Steps to reproduce:

1. Import data_test.sql in DB;

2. Check table timeperiods, column start_date

3. Open maintenance period configuration form in frontend

4. Click button ‘Update’

Result: table timeperiods, column start_date updated on ‘1920’

Expected: Filed must be equal to - current date (default value).