Update php_fast_cache.php

I got error for the first time running if config like this:

phpFastCache::$storage = "auto";
phpFastCache::$autosize = 50;
phpFastCache::$path = SRV_ROOT.CACHE;
phpFastCache::$securityKey = md5("cache.storage.jkdofjgh53kdod987");
phpFastCache::$server = array(
                       array("localhost",11211,30),
                       array("localhost",11211,70)
                   ); 


Warning: file_get_contents(/Applications/MAMP/htdocs/xyz/cache//e97c2fd1cbb77bf3bb5e598d1b4de426//config.D.cache.ini) [function.file-get-contents]: failed to open stream: No such file or directory in /Applications/MAMP/htdocs/xyz/mylibrary/php_fast_cache.php on line 208

File does not exists.

If on second run does not got this problem. Maybe it's a minor bug.

thanks..