vorbisdec: Check bark_map_size.

This fixes potential divisions by zero and out of array accesses.

Reported-by: Dale Curtis <dalecurtis@chromium.org>
Found-by:  <inferno@chromium.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 2c16bf2d)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>