[FIX] survey: fix survey statistics computation
[FIX] survey: fix survey statistics computation

Purpose
=======

This commit fixes the shared dict in the survey statistics computation that
causes surveys to incorrectly share the same stats when computed in batch.
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo