process_karaoke_effects: use long long for timestamps
process_karaoke_effects: use long long for timestamps

Our frame timestamps are long long. Don't truncate them to int here.

This also avoids overflow in (tm_end - tm_start) if \k... tag arguments
are big, although, of course, parse_tags still reads them in as doubles
to begin with and their conversion from double may still be undefined.

astiob/libass,MrSmile/libass,xbmc/libass,astiob/libass,Akemi/libass,ShiftMediaProject/libass,ShiftMediaProject/libass,Akemi/libass,Akemi/libass,MrSmile/libass,xbmc/libass,libass/libass,libass/libass