Description:
------------
While I was looking into this bug
https://bugs.php.net/bug.php?id=70520
I found mcrypt_decrypt() sometimes raises "String is not zero-terminated" error. It seems mcrypt_decrypt() returns broken data sometimes also. It makes session decode fail on occasion.

Warning:  String is not zero-terminated (�J?w�fr,�:v�handler) (source: /home/yohgaki/git/oss/php.net/php-src/Zend/zend_execute.c:2061) in /home/yohgaki/workspace/ext/git/oss/php.net/php-src/tt2.php on line 20

Warning:  session_start(): Failed to decode session object. Session has been destroyed in /home/yohgaki/workspace/ext/git/oss/php.net/php-src/tt2.php on line 38

Tested by CLI server. If I don't use mcrypt_decrypt/encrypt(), the test code will not raise errors.

Test script:
---------------
<?php
ob_start();
error_reporting(E_ALL | E_STRICT);
ini_set('session.save_path', '/tmp');
ini_set('display_errors', true);

class EncryptedSessionHandler extends SessionHandler
{
    private $key;

    public function __construct($key)
    {
        $this->key = $key;
    }

    public function read($id)
    {
        $data = parent::read($id);

        return mcrypt_decrypt(MCRYPT_3DES, $this->key, $data, MCRYPT_MODE_ECB);
		//return $data;
    }

    public function write($id, $data)
    {
        $data = mcrypt_encrypt(MCRYPT_3DES, $this->key, $data, MCRYPT_MODE_ECB);

        return parent::write($id, $data);
    }
}

ini_set('session.save_handler', 'files');
$key = substr(sha1(random_bytes(24)), 0, 24);
$handler = new EncryptedSessionHandler($key);
session_set_save_handler($handler, true);

echo '<pre>';
session_start();
$_SESSION['key'] = 1234;
var_dump($_SESSION);
echo session_id() . PHP_EOL;
session_regenerate_id(true);
echo session_id() . PHP_EOL;