matroskadec: fix out of bounds write

Signed-off-by: Janne Grunau <janne-libav@jannau.net>
(cherry picked from commit 723229c11f1400e6a09c8a1c9c27193f376eb1d1)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit d51c7b4cbe022f6b3b026735dc7e29eb50bbf129)

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