Description:
------------
When trying to retrieve an array from Memcached the script freezes until it dies because of no more memory.

ante@Bagheera:~/php-test$ nc localhost 11211
get a
VALUE a 6 2
[]

Everything works fine when using something different from an array, like an integer.

Reproduce code:
---------------
<?php
$m = new Memcached;
$m->addServer("localhost", 11211, 0);
$m->setOption(Memcached::OPT_SERIALIZER, Memcached::SERIALIZER_JSON);
$m->set("a", array());
var_dump($m->get("a"));

Expected result:
----------------
array(0) {
}

Actual result:
--------------
PHP Fatal error:  Out of memory (allocated 628883456) (tried to allocate 2513135616 bytes) in /home/ante/php-test/m.php on line 6
PHP Stack trace:
PHP   1. {main}() /home/ante/php-test/m.php:0
PHP   2. Memcached->get() /home/ante/php-test/m.php:6