[FIX] hr_holidays: ignore unconfirmed leaves in current leave status

As of this commit, only confirmed leaves will be considered when computing the
current leave or absence of an employee. Additionally, a bug in the is_absent
search implementation was fixed: before this commit, the same results were
returned for absent and non-absent searches.

opw-2877328

closes odoo/odoo#118475

X-original-commit: 37f2fc5c
Signed-off-by: Kevin Baptiste <kba@odoo.com>
Signed-off-by: De Caluwé Tom (tdc) <tdc@odoo.com>