improve null str test

<?php

error_reporting(E_ALL);

$key = "hello\0world";

$val = "foo\0bar";

$bdict = new bdict();

$bdict->set('hello', new bstr("foo\0bar"));

echo strlen($bdict->get('hello')->get()) . "\n";

echo bin2hex($bdict->get('hello')->get());

$bdict->set($key, new bstr($val));

echo strlen($bdict->get($key)->get()) . "\n";

echo bin2hex($bdict->get($key)->get());

exit(0);

?>