timeline: Avoid NULL dereference if Data Reference Box is absent.
timeline: Avoid NULL dereference if Data Reference Box is absent.

maki-rxrz/L-SMASH,silverfilain/L-SMASH,l-smash/l-smash,canbal/l-smash,silverfilain/L-SMASH,silverfilain/L-SMASH,l-smash/l-smash,l-smash/l-smash,maki-rxrz/L-SMASH,canbal/l-smash