Fix implicit declaration of function 'isom_write_mdat_size'.
Fix implicit declaration of function 'isom_write_mdat_size'.

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