[FIX] web: aceField with a value of false

Have a record with a field displayed with the aceField.
That field should have a value of false (ie: unset).
Display that record on a form view.

With the pager, go on to the next record.

Before this commit, a write was triggered because the aceField considered itself as changed
even though we did not do anything.
This was because the value of false was compared to the ace value (empty string) when leaving the record.
Being different, this triggered the current record to be updated and saved.

After this commit, a false value is locally transformed to the empty string when checking if the field has
some changes. Hence, there is no write triggered.

opw-3326914

closes odoo/odoo#121634

Signed-off-by: Lucas Perais (lpe) <lpe@odoo.com>