Fix warning in subscribers/subscriptions list pages where we attempted to call free() an ArrayWrapper after it was used up, thus trying to forward the call to a nonexistent object.

Removed the free calls (unneeded since destructors now work), and added an error check w/ logging & an exception for future attempts to forward calls to nonexistent object.

lib/arraywrapper.php

@@ -76,6 +76,10 @@ class ArrayWrapper
     function __call($name, $args)
     {
         $item =& $this->_items[$this->_i];
+        if (!is_object($item)) {
+            common_log(LOG_ERR, "Invalid entry " . var_export($item, true) . " at index $this->_i of $this->N; calling $name()");
+            throw new ServerException("Internal error: bad entry in array wrapper list.");
+        }
         return call_user_func_array(array($item, $name), $args);
     }
 }