Submitting the administrative user delete confirmation form twice results in faulty operation of $account thought to be uid 0

When a user is deleted from /admin/user/user in a way that submits/confirms the delete users form twice or more, it results in the user_delete() function to be called several times, which in return invokes the 'delete' op for other modules with $account being set to FALSE/0 => this yields other modules acting on the anonymous user account 0.

Reconstruct:

1. Go to /admin/user/user
2. Toggle a test user to be deleted
3. Choose 'delete the selected users' and click 'Update'
4. Click 'Delete All' in the confirmation form
5. Wait a few seconds or immediately after click on 'Delete All' in the submitting form

What happens is that the form will submit and invoke the user_delete() function which will load the user:

function user_delete($edit, $uid) {
  $account = user_load(array('uid' => $uid));

This is ok for the first time that the form is submitted, but in the second time that the form is submitted while being executed, that user no longer exists because it has been deleted already by the former, original, 'Delete All' button click.
So now, in the 2nd time, the user has clicked the 'Delete All' button the user entry doesn't exist, hence user_load() returns FALSE and sets $account accordingly. Although, this does not stop from the rest of the code to execute and when other modules are invoked, such as:

function user_delete($edit, $uid) {
  // continued rest of the function code:
  user_module_invoke('delete', $edit, $account);
}

$account is actually 0 due to weak typing, resulting in module's being invoked and working accidentally on uid 0.