Fix memory leak in zim_Phalcon_Tag__inputField()

Test case:

```php
$di = new \Phalcon\Di\FactoryDefault();
echo Phalcon\Tag::submitButton('ľščťžýáíéôňď'), PHP_EOL;
```

Result:
```
<input type="submit" value="ľščťžýáíéôňď" />
[Sun Dec 15 21:28:24 2013]  Script:  '/home/vladimir/workspace/cphalcon/1681.php'
/home/vladimir/workspace/cphalcon/ext/kernel/memory.c(350) :  Freeing 0x7F29ED5A84E0 (32 bytes), script=/home/vladimir/workspace/cphalcon/1681.php
```