UUID does not get saved to a file after v660

If you do a comparison between v660 and 78ad32c6d202a877e94d023df72a598193cbb91d then you can see that the GetUUID function in SharedConfig.cpp has changed and now, if the file does not already exist then it is never created. This is incorrect behaviour as the user can now never specify that they want whatever UUID is created for them to be persisted.

This should be fixed and made to work in the same manner that it used to.