Add zero padding to filename suffix in splitByFile()

Patch thanks to Alexandr Agranovsky <alesso@alesso.ru>
Correct ZERO suffix

Signed-off-by: Jari Aalto <jari.aalto@cante.net>
Merge pull request #4 from jaalto/zero-padded

Add zero padding to filename suffix in splitByFile()

Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>