[FIX] base: avoid prefetching all the fields when getting context
[FIX] base: avoid prefetching all the fields when getting context

When getting the context of res_users, all the fields are read but if
the schema is being modified and the modifications are not yet commited
in the database, this leads to a bad query.

With this commit, a read is used to fetch only the needed fields.

Thanks to @RCO for finding this issue that only occurs in specific
planetary alignment.

closes odoo/odoo#27263
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo