[FIX] base: no crash when setting wrong relation to m2m
[FIX] base: no crash when setting wrong relation to m2m

Before this rev., in the ir.model.fields form view, it crashed
when the user specified an invalid model name as a relation for
fields of type many2many (the onchange crashed). This rev. displays
a warning instead.

opw 1837401

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo