in case of require an empty class for ClassLoader

for some reason the function loadClass is requiring the $class which has no value.

It cause following error,I made some tweaks for them to avoid the error.

./error.log:2013/08/15 14:49:20 [error] 21114#0: *5396972 FastCGI sent in stderr: "PHP message: PHP Fatal error:  require(): Failed opening required '' (include_path='.:/usr/share/php:/usr/share/pear') in /var/www/www/releases/20130729091149/app/bootstrap.php.cache on line 1068" while reading response header from upstream, client: 1.1.1.1, server: www.test.com, request: "POST / HTTP/1.1", upstream: "fastcgi://unix:/var/run/www.php5-fpm.socket:", host: "www.test.com"

bootstrap.php.cache line1068:
```
    public function loadClass($class)
    {
        if ($file = $this->findFile($class)) {             <-------line 1068
            require $file;

            return true;
        }
    }
```