The goal of the to_check checkbox in the reconciliation widget is to set the to_check field present on the move that will be created. However since the UI is not perfect, the to_check checkbox was added on the wizard when we create a new line in the widget, which cause the following problem: what if we select to_check on line1 and then deselect it on line2, previously it was not possible to do this, a warning was thrown to tell the user that he had some line with to_check set and some other not. A better way to do this, and more user friendly is by preventing the user from deselecting the checkbox if some other line has the to_check value set.

closes odoo/odoo#33956

Signed-off-by: Cedric Snauwaert (csn) <csn@openerp.com>