[FIX] web: multi edit in custom groupby list view

Steps to follow

  - Go to Accounting > Accounting > Sales (account.move.line model)
  - Remove any existing group by
  - Group by Products
  - Select multiples lines of the same product
  - Try to modify the account of the select line
  -> `this.localData[value] is undefined

Cause of the issue

  When grouping by a field not in the view, `list.__data` contains the
  groupedBy field value because we fetched the group through a web_read_group

Solution

  Filter out absent fields before creating the group datapoint

opw-2784995

closes odoo/odoo#88032

Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>