[FIX] l10n_ch: human readable ISR number set to False

The condition on computation of `l10n_ch_isr_number_spaced` was not in line anymore with
`l10n_ch_isr_number` computation.
With fixes on the ISR number the use of `l10n_ch_isr_postal` is rightly not
mandatory anymore.

This lead to an empty field, visible on the ISR report.

closes odoo/odoo#66854

Signed-off-by: Josse Colpaert <jco@openerp.com>