QR code for adding a node rejected if no user & pass in URI
**Describe the bug**
Attempting to scan an xmrrpc URI which does not contain a username & password is rejected as invalid.

**To Reproduce**
Steps to reproduce the behavior:
1. Go to 'Connection and Sync' -> 'Manage nodes' -> 'Add new node'
2. Scan the example QR code at the bottom

The issue appears to originate from [here](https://github.com/cake-tech/cake_wallet/blob/331d6ee64836f52486a7fb43aee2adddd7efb873/lib/view_model/node_list/node_create_or_edit_view_model.dart#L230).

**Expected behavior**
The node should be added with username & password left blank.

**Platform:**
- OS: Android 13, GrapheneOS
- Device: Google Pixel 4a
- Cake Wallet Version: 4.20.0

**Additional context**
An example QR code:

![qr](https://github.com/user-attachments/assets/e3b2311d-4bfc-48f0-be02-054fef1750ff)
