cache_get is called, but cache value never set

The _sitemenu_overview() starts with a call to cache_get (see below), but the cache value is never set!

function _sitemenu_overview($type = 0, $mode = 'page') {
  $n=0;
  $vocabularies = _sitemenu_get_vocabularies($type);
  foreach ($vocabularies as $vocabulary) {
    $tree_nodes = unserialize(cache_get("sitemenu:tree_nodes_$type". $vocabulary->vid));

attached patch tries to correct this behavior and also to make sure the cache ID is unique by concatenating $mode as well. Patch code seems to work- at least in as much as no obvious errors are generated ;-)