[FIX] point_of_sale: already reconciled stock_account_move_line

When the customer use Anglo-Saxon stock valuation and have already
reconciled some `account.move.line` related to an open `pos.session`,
closing the session will fail.
(You are trying to reconcile some entries that are already reconciled)

Now, the reconciled lines are ignored.
The inventory valuation is still correct as these lines were already
reconciled.

opws:
2374559
2376187
2377958
2391395
2425197

closes odoo/odoo#64415

Signed-off-by: Simon Goffin (sig) <sig@openerp.com>