demux: mp4: fix heap read overflow in vide handler
demux: mp4: fix heap read overflow in vide handler

(cherry picked from commit 3417a40402599d56395fd2ae0e55baec25e41a52)
Signed-off-by: Jean-Baptiste Kempf <7b85a41a628204b76aba4326273a3ccc74bd009a@videolan.org>

jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2