drush_choice_multiple() does not allow selecting if $max is NULL

drush_choice_multiple seems broken when $defaults is FALSE and $max is not set. The problem code seems to be here:

    // If the user selected too many options, drop the oldest selection.
    if (count($selections) > $max) {
      array_pop($selections);
    }

Should be:

    if (isset($max) && count($selections) > $max) {
      array_pop($selections);
    }

Otherwise, every selection the user makes then gets unset again in this code.