Rockboxutility fails to create voices when encountering unpronouncable filenames

[fennectech]

https://www.rockbox.org/tracker/index.php?do=details&action=details.addvote&task_id=13156
Here is a link to the bug report i made on flyspray    a workarround is removing unpronouncable filenames but this is irritating at best and downright unacceptable if you have thousands of unpronouncable filenames spaced throughout your library.   rbutil should continue after failing to encode a file rather than bailing.