[IMP] hr_holiday: Don't check access rights on allocation if no employee

If there are no employee set on the allocation request and if the user
is a leave officer, don't check the access rights as it would lead to
a traceback.

addons/hr_holidays/models/hr_leave_allocation.py

@@ -486,6 +486,8 @@ class HolidaysAllocation(models.Model):
     def _check_approval_update(self, state):
         """ Check if target state is achievable. """
         current_employee = self.env['hr.employee'].search([('user_id', '=', self.env.uid)], limit=1)
+        if not current_employee:
+            return
         is_officer = self.env.user.has_group('hr_holidays.group_hr_holidays_user')
         is_manager = self.env.user.has_group('hr_holidays.group_hr_holidays_manager')
         for holiday in self: