Fix segfault when starting ctld w/out dbd

If the dbd comes up after a job array has been submitted to the
controller, the controller calls _update_job_tres() which calls
assoc_mgr_set_tres_cnt_array() which allocates memory for the job's
tres_alloc_cnt. The job array gets scheduled, but job_array_split()
doesn't NULL out the pending job's tres_alloc_cnt, so both the array
task and the pending array job are pointing to the same memory. The
array task calls job_set_alloc_tres() which free's the running job's
tres_alloc_cnt and now the pending array job is pointing to bad memory
and when the array splits again the new array task tries to free
tres_alloc_cnt in job_set_alloc_tres() and segfaults.

Bug 5604