Fix encoder crash with non-positive sample rates.
Fix encoder crash with non-positive sample rates.

Input files with sampling rate 0 are useless and can make
libvorbis access invalid memory because the logic in
_vp_psy_init (and probably other functions) isn't prepared for
it. A sanity check lets the library refuse those inputs
gracefully in the initialization functions before they can
do harm.

Patch by Martin Steghöfer <martin@steghoefer.eu>

Fixes #2078
Bug-Debian: https://bugs.debian.org/716613


svn path=/trunk/vorbis/; revision=19422

ShiftMediaProject/vorbis,ksophocleous/vorbis,youfearm3/vorbis,ksophocleous/vorbis,ShiftMediaProject/vorbis,nicolaichuk/vorbis,mwgoldsmith/vorbis,nicolaichuk/vorbis,erikd/vorbis,felipebetancur/vorbis,ksophocleous/vorbis,youfearm3/vorbis,ShiftMediaProject/vorbis,mwgoldsmith/vorbis,eidy/vorbis,erikd/vorbis,emscripten-ports/Vorbis,ShiftMediaProject/vorbis,eidy/vorbis,erikd/vorbis,emscripten-ports/Vorbis,mwgoldsmith/vorbis,felipebetancur/vorbis,emscripten-ports/Vorbis,nicolaichuk/vorbis,emscripten-ports/Vorbis,nicolaichuk/vorbis,eidy/vorbis,felipebetancur/vorbis,ShiftMediaProject/vorbis,mwgoldsmith/vorbis,erikd/vorbis,ksophocleous/vorbis,felipebetancur/vorbis,eidy/vorbis,youfearm3/vorbis,ShiftMediaProject/vorbis,youfearm3/vorbis