[FIX] hr_holidays: fix logic of a onchange on leave allocation

- When changing the `holiday_type` of a leave allocation while having an
  employee set and if this `holiday_type` has as its value `employee`
  the field `employee_id` is set to False.

  This is not the intended behavior. We want the field `employee_id`
  to be filled if the `holiday_type` is set to `employee`.

closes odoo/odoo#32886

Signed-off-by: Denis Ledoux <beledouxdenis@users.noreply.github.com>

addons/hr_holidays/models/hr_leave_allocation.py

@@ -243,8 +243,8 @@ class HolidaysAllocation(models.Model):
 
     @api.onchange('holiday_type')
     def _onchange_type(self):
-        if self.holiday_type == 'employee' and not self.employee_id:
-            if self.env.user.employee_ids:
+        if self.holiday_type == 'employee':
+            if not self.employee_id and self.env.user.employee_ids:
                 self.employee_id = self.env.user.employee_ids[0]
         elif self.holiday_type == 'department':
             if self.env.user.employee_ids: