Correctly handle multiple files in a single CUE

[ FIXED ]  Fixed the last index NOT being saved when splitting
multiple files from the same CUE file

[ ENHANCEMENT ]  Using `shnsplit's' '-c' argument is now obtained
dynamically for each operation to process.  This makes it possible
to have file tracknumber which increment correctly in a directory
when there are multiple CUE files for one album and each CUE file
labels each track starting from '01'