#73867, fixed warning, patch by bobathtmldotcom

includes/bootstrap.inc

@@ -336,7 +336,7 @@ function cache_get($key) {
     // cache timer.  The cache variable is loaded into the $user object by
     // sess_read() in session.inc.
     else {
-      if ($user->cache > $cache->created) {
+      if (isset($user->cache) && ($user->cache > $cache->created)) {
         // This cache data is too old and thus not valid for us, ignore it.
         return 0;
       }