More defensive directory checking in _check_execution.
More defensive directory checking in _check_execution.

Probably not needed - only hit the error condition because of other bugs - but I guess it is not hurting anything.

ssorgatem/pulsar,galaxyproject/pulsar,jmchilton/pulsar,natefoo/pulsar,natefoo/pulsar,galaxyproject/pulsar,jmchilton/pulsar,ssorgatem/pulsar