Fix EZP-22991: Added file exists control for parse method

After update to 2014.03 version, when functional tests are launched the path of tr files is wrong. This PR add a file exists check before to launch the parseString method. 

This is not the better solution but I'm not sure if I can thrown an Exception (if so which one?) and, above all, if I can fix the path directly in the parse method. I don't know if this method is used elsewhere and if in other cases the path works fine.

Any suggestions in order to fix the issue are more than welcome.