Bug in "poll_user" when deleting user (when multiple users have voted in the poll)

When a user account is deleted, the "poll_user" function below is executed where it updates the "{poll_votes}" table to set the UID to 0 for the deleted user.

A problem arises when you try to delete more than one user, where each user has voted in the same poll. The code below will try to set the UID to 0, however that tuple may already exist in the table, so the db_query will fail and report an error.

function poll_user($op, &$edit, &$user) {
  if ($op == 'delete') {
    db_query('UPDATE {poll_votes} SET uid = 0 WHERE uid = %d', $user->uid);
  }
}

How to reproduce:

1. Create at least two user accounts.

2. Create a poll, and have both user accounts vote in the poll.

3. Delete one user account; all should be fine when the "poll_user" function exeuctes.

4. Delete the other user account, and a "user warning: Duplicate entry ...." database error will occur.

Consequences:

The "user warning: Duplicate entry ...." database error will occur every time a new user is deleted (where they had previously voted in the same poll). Additionally, the deleted UID's will remain in the "{poll_votes}" table since they can't be removed.

Possible Solution:

Instead of trying to set the UID back to 0, it would be better to completely remove the user entry since, after all, the account is deleted. This will keep the {poll_votes} table clean.