[FIX] web: action manager and modals should interact correctly
[FIX] web: action manager and modals should interact correctly

Before this commit, the action manager could in some case have a
reference of a modal dialog, even after it has been destroyed (for
example, when the "X" button has been clicked to close a modal).

Unfortunately, it has some unexpected consequences, for example, the
do_push_state method check the existence of self.dialog to update the
url.

hip-odoo/odoo,dfang/odoo,hip-odoo/odoo,ygol/odoo,hip-odoo/odoo,ygol/odoo,ygol/odoo,ygol/odoo,dfang/odoo,dfang/odoo,hip-odoo/odoo,ygol/odoo,hip-odoo/odoo,dfang/odoo,dfang/odoo,dfang/odoo,ygol/odoo,hip-odoo/odoo,ygol/odoo