streams/sdo: Special case for 0 and 1 arg versions

This changes sdo to have special cases for 0 and 1 args, calling
bit-bucket in the 0-arg case, and the child directly in the second case.

Fixes #398.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Merge pull request #469 from algernon/f/sdo-special-cases

streams/sdo: Special case for 0 and 1 arg versions