chd updates: [MetalliC]
- Bugfixed byte order for GD-ROM audio tracks so FLAC compression is effective
- Fixed uninitialized struct on MSVC (and possibly other) builds


nw: this will change the SHA1s of every GD-ROM CHD in MAME; a patch to reflect that is pending (the old images still work, they just take a little more space than is necessary).  "chdman copy" suffices to upgrade; no downloading is necessary.