demux: mp4: fix last chunk size computation (fix #12362)
demux: mp4: fix last chunk size computation (fix #12362)

(cherry picked from commit 8a0493add9682187192cc3dab514294ad0b9f541)
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