Better checking to make sure structure elements exist

src/common/slurm_step_layout.c

@@ -388,7 +388,7 @@ extern int slurm_step_layout_destroy(slurm_step_layout_t *step_layout)
 int slurm_step_layout_host_id (slurm_step_layout_t *s, int taskid)
 {
 	int i, j;
-	if (taskid > s->task_cnt - 1)
+	if (!s->tasks || !s->tids || (taskid > s->task_cnt - 1))
 		return SLURM_ERROR;
 	for (i=0; i < s->node_cnt; i++)
 		for (j=0; j<s->tasks[i]; j++)