[FIX] hr_work_entry: make _error_checking faster

Calls to `_error_checking()` would look for every work entries between 2
dates, even if we were only modifying one employee's.

Because of that the leave creation on big production database would take
a long time.

Now the method allows for filtering to the employees.

task-3142610

closes odoo/odoo#110559

Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>