[FIX] l10n_fr_hr_payroll: report "Fiche de paye"

Avoids getting False for the field end_date (Sortie) in case of no end date specified on the contract. opw 614624
[FIX] l10n_fr_hr_payroll: bad copy-paste in 69c1333
Merge branch '7.0' of https://github.com/odoo/odoo into 7.0-win32