[FIX] base/ir_ui_view: Raise ValidationError when creating views without arch/type

Closes #16973

Steps to reproduce:

1) Go to Settings -> Technical -> User Interface -> Views
2) Create a new view and give only name, leave fields View Type and arch_base empty.
3) Exception occures

Current behaviour:
- The user gets an exception with a full stacktrace.
Expected behaviour:
- The user should get a warning

odoo/addons/base/ir/ir_ui_view.py

@@ -341,6 +341,8 @@ actual arch.
             else:
 
                 try:
+                    if not values.get('arch') and not values.get('arch_base'):
+                        raise ValidationError(_('Missing view architecture.'))
                     values['type'] = etree.fromstring(values.get('arch') or values.get('arch_base')).tag
                 except LxmlError:
                     # don't raise here, the constraint that runs `self._check_xml` will