select/cray: zero reservation ID is not an error

This avoids meaningless error messages that warn about a zero reservation ID:

 [2011-04-07T15:31:26] _slurm_rpc_submit_batch_job JobId=2870 usec=33390
                       ... a minute later the user decides to scancel the queued job:
 [2011-04-07T15:32:34] error: JobId=2870 has invalid (ZERO) resId
 [2011-04-07T15:32:34] sched: Cancel of JobId=2870 by UID=21770, usec=230

To keep things simple, that test has been removed.

(The patch is in particular also necessary since now job_signal() may trigger
 a basil_release() of a pending job which has no ALPS reservation yet.)