slurm_find_jobs incorrect return on empty joblist

[gdevenyi]

After fixing parsing in https://github.com/pipitone/qbatch/commit/3f1de91412279bac4f7dc18ad6f4ab4684c1c570

This line: https://github.com/pipitone/qbatch/blob/master/qbatch/qbatch.py#L275 is returning two items instead of one.