Fix for ParallelCmds.join when a cmds has failed.
Fix for ParallelCmds.join when a cmds has failed.

Prevent calling join() on an AtomicCmd that has not been started,
due to the failure of an earlier command in the sequence.

MikkelSchubert/paleomix,MikkelSchubert/paleomix,MikkelSchubert/paleomix