[FIX] base: avoid generating invalid user group view

When no `base.module_category_user_type` Application is found, the group
view was generated with the domain `[('', '!=', <int>)]`, which is will
fail view validation.

This situation happen during database migration or if the module category
is deleted.

odoo/addons/base/models/res_users.py

@@ -885,7 +885,10 @@ class GroupsView(models.Model):
                             xml3.append(E.field(name=field_name, **attrs))
 
             xml3.append({'class': "o_label_nowrap"})
-            user_type_attrs = {'invisible': [(user_type_field_name, '!=', group_employee.id)]}
+            if user_type_field_name:
+                user_type_attrs = {'invisible': [(user_type_field_name, '!=', group_employee.id)]}
+            else:
+                user_type_attrs = {}
 
             xml = E.field(
                 E.group(*(xml1), col="2"),