Use stored value for One2Many changed without initial value

If the client does not send the value for the One2Many (it happens when it is
not modified), we must assume that it has the stored value unchanged. Otherwise
the current records are considered as to be added but with only their changed
values.

issue8605
review265901016

trytond/model/modelview.py

@@ -775,7 +775,7 @@ class ModelView(Model):
                         value = value.id
             elif field._type == 'one2many':
                 targets = value
-                init_targets = list(init_values.get(fname, []))
+                init_targets = list(init_values.get(fname, targets))
                 value = collections.defaultdict(list)
                 value['remove'] = [t.id for t in init_targets if t.id]
                 for i, target in enumerate(targets):