privatemsg_message_change_recipient() does not pass $context to hook_privatemsg_block_message()

In implementing some custom ignoring and blocking logic, I stumbled into what appears to be an oversight.

In privatemsg.module in the privatemsg_message_change_recipient() function, no context is passed for replies when 'hook_privatemsg_block_message' is invoked.

function privatemsg_message_change_recipient($mid, $uid, $type = 'user', $add = TRUE) {

  $thread_id = db_result(db_query('SELECT thread_id FROM {pm_index} WHERE mid = %d', $mid));
  if ($add) {
    // Only add the recipient if he does not block the author.
    $author_uid = db_result(db_query('SELECT author FROM {pm_message} WHERE mid = %d', $mid));
    $recipient = privatemsg_user_load($uid);
    $user_blocked = module_invoke_all('privatemsg_block_message', privatemsg_user_load($author_uid), array(privatemsg_recipient_key($recipient) => $recipient));
    if (count($user_blocked) <> 0) {
      return;
    }

    [.... the rest of the function ...]

In theory you can just compare thread_id to mid to see if this is a reply or a new message, and if it is a reply, you can pass the proper context.

Patch forthcoming.