[FIX] broken inference of groupby groups in search view filters
[FIX] broken inference of groupby groups in search view filters

Before the valpocalypse, filter contexts were "literal" (parsed
objects) when reaching the search view, and `.attrs.context.group_by`
would return the right thing (namely the group_by attribute of the
context object).

After the valpocalypse, contexts & domains on view fields (and
filters) are not evaluated on the Python side anymore and reach view
objects as strings, the access chain above thus always returns a falsy
value (undefined) as strings don't have a .group_by.

Fix FilterGroup to correctly parse filter's @context before trying to
see if it has a group_by.


akretion/openerp-web,akretion/openerp-web,akretion/openerp-web,havt/openerp-web,havt/openerp-web,havt/openerp-web,havt/openerp-web,havt/openerp-web