[FIX] core: onchange() snapshot should only contain expected fields

This fixes an issue with an override of onchange() on account.asset,
which asks for less fields to be considered in the snapshot.  This also
guarantees that onchange() does not return values for unexpected fields.

Part-of: odoo/odoo#116779

odoo/models.py

@@ -6484,7 +6484,8 @@ class BaseModel(metaclass=MetaModel):
 
         # update snapshot0 with changed values
         for name in names:
-            snapshot0.fetch(name)
+            if name in nametree:
+                snapshot0.fetch(name)
 
         # Determine which field(s) should be triggered an onchange. On the first
         # call, 'names' only contains fields with a default. If 'self' is a new