[FIX]account_asset: fix problem when we validate the last depreciation line it...

[FIX]account_asset: fix problem when we validate the last depreciation line it was closing the asset without checking if all depreciation lines was validated

lp bug: https://launchpad.net/bugs/939390 fixed

bzr revid: csn@openerp.com-20121115110448-y0csyrbgpexam0kt