User file stream close callback function.
void CALLBACK FileCloseProc(
With a buffered file stream, this function is called as soon as reading reaches the end of the file. If the stream is freed before then, this function could be called while its FILEREADPROC function is in progress. If that happens, the FILEREADPROC function call should be immediately cancelled.
BASS_StreamCreateFileUser, BASS_FILEPROCS structure