[FIX] survey: do not always get answer_score

Calling `_get_answer_score_values` on each question creation or update is
not necessary if value is already provided.

Followup of odoo/odoo@0d32ed45aebe2721073580ddae68ec4a8c1499d6

closes odoo/odoo#68500

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>