navigation: split chapter mark counting to separate function
navigation: split chapter mark counting to separate function

ShiftMediaProject/libbluray,mwgoldsmith/bluray,tourettes/libbluray,Azzuro/libbluray,tourettes/libbluray,tourettes/libbluray,ace20022/libbluray,Azzuro/libbluray,Azzuro/libbluray,ShiftMediaProject/libbluray,tourettes/libbluray,ace20022/libbluray,ShiftMediaProject/libbluray,mwgoldsmith/bluray,ace20022/libbluray,ace20022/libbluray,mwgoldsmith/bluray,ShiftMediaProject/libbluray,mwgoldsmith/bluray,Azzuro/libbluray