vorbisfile has a flaw where a bad link is not initialized [proper

vorbisfile has a flaw where a bad link is not initialized [proper
behavior], but it would attempt to initialize and play that link
anyway, getting a segfault.  The easiest way to deal was to improve
libvorbis's error checking on dsp initialization if an app (in this
case, vorbisfile) tries to call init on a blank vorbis_info structure.

read and seek calls will now return 'OV_EBADLINK' in this case.

Monty

svn path=/trunk/vorbis/; revision=5278