validation Individual user logout

Reviewed the patch with the Drupal 9 core version. The patch prevents the page break for the Invalid user logout. Attached screenshot on after the patch is applied.

Moving the issue to RTBC.

Thanks for the work to date. That said, the proposed patch explicitly checks for characters within parentheses, which IMHO isn't really validating that the specified user exists. I would suggest that the code should:

1. Check only for digits within the parentheses
2. Actually try to load the user with the provided uid

if both of those are, I would consider the specified user to be properly validated.