Remote FS swallows API errors when the API token expired

Summary

When the token expires, API starts returning non-authorized errors and the remote FS inmplementation interprets that as a missing file.

Steps to reproduce

  1. Create a token and set it to expire today.
  2. Wait a day (maybe this could be sped up if you revoke the token)
  3. Try to use remote FS
  4. See an error about non-existing file

What is the current bug behavior?

Error about non-existing file.

What is the expected correct behavior?

Error about unauthenticated request to the API.

Relevant logs and/or screenshots

Extension_Development_Host_-vscode__GitLab

Possible fixes

Change the implementation of nullIf40x() method.

/cc @firelizzard