[FIX] expression: Better Binaries logs

When building a domain `(=|!=)` with
a Binary field stored in attachment and
the right part of the domain is not null,
the full binary content is logged, giving
the logs a huge size.

Now, the content of the binary is cropped to
20 chars as it is useless to log more.

opw-2527629

closes odoo/odoo#70699

X-original-commit: d54b30bb
Signed-off-by: Xavier Dollé (xdo) <xdo@odoo.com>
Signed-off-by: Raphael Collet (rco) <rco@openerp.com>