SOLIDPOD EG BUG: add permission to specific resource fails if resource not found

[jesscmoore]

Describe the Bug

In the solidpod example demo, choosing the button 'adding/deleting permissions for a specific resource' fails to load page. This occurs on:

• a new account when the file keyvalue/key-value.ttl hasn't yet been created and the user chooses 'add/deleting permissions for a specific resource.
• any user's account when the user chooses 'add/delete permissions for any resource' and enters the name of a file with a typo such that the file cannot be found.

To Reproduce

1. Run solidpod example, demopod
2. Login as new user, run solid setup wizard to create account.
3. Select 'adding/deleting permissions for a specific resource"
4. App hangs perpetually on loading widget screen with no error message in app or console.

Expected Behaviour

The file not exist exception should probably be used. A popup could display advising that the file does not exist.

Expected Behaviour

The not exists exception should be thrown and caught by the future called to retrieve permissions.

Screenshots

Eg if user enters a filename with a typo:

App Version: solidpod 0.9.13 example
Flutter Version: 3.38.7

Closing Criteria

Checklist for closing the issue:

• No errors from make prep
• All tests pass make qtest
• [Issue specific requirements.]