[FIX] web: form: restore value when onchange returns an error

In a form view, have a field with an onchange that returns an
error. Before this commit, the error was displayed but the
faulty value that triggered the onchange (and thus the error)
was still displayed in the UI (even though in the model, the
previous value was still set).

This commit enforces an update of the UI when an error occurs,
such that the previous, valid, value is displayed again.

For instance:
Go to a customer invoice, open the Actions menu, click on
"generate a payment link", in the dialog, set an high amount.

Task~3498849

Part-of: odoo/odoo#134792