Incorrect confirmation during Configure Default channel

[michalina-graczyk]

1. Install Saleor Invoices app
2. Go into that app
3. In Configure Default channel channel area don't fill anything
4. Press save channel notification button

Current result: I am getting a popup Saved app configuration Exoected result: User can't save empty fields, or some of them are required. It might be confusing for a user what is saved