write song don't support sample filenames which contains sub directory.

normal hydrogen drumkits rootdir contains all samples.
if you create subdirs for instruments like into the gscw drumkits, hydrogen is unable to write the right path into the songfile.
if you open a song with a drumkit with subdirs the the sample won't found.

*you can load such drumkits with the sondlibrary.
*save such drumkits fail, or produce a drumkits without subdirs.
*save a song fails. (wrong sample path will write into the songfile)