Fix setting min_cpus to correct value when no task count is given.

Bug 3888

src/slurmctld/job_mgr.c

@@ -6797,7 +6797,14 @@ extern int validate_job_create_req(job_desc_msg_t * job_desc, uid_t submit_uid,
 	if ((job_desc->overcommit == (uint8_t) NO_VAL) &&
 	    (job_desc->min_cpus != NO_VAL) &&
 	    (job_desc->num_tasks > job_desc->min_cpus)) {
-		job_desc->min_cpus = job_desc->num_tasks;
+
+		if (job_desc->num_tasks != NO_VAL)
+			job_desc->min_cpus = job_desc->num_tasks;
+		else if (job_desc->min_nodes != NO_VAL)
+			job_desc->min_cpus = job_desc->min_nodes;
+		else
+			job_desc->min_cpus = 1;
+
 		if (job_desc->cpus_per_task != (uint16_t) NO_VAL)
 			job_desc->min_cpus *= job_desc->cpus_per_task;