Merge branch 'bugfix' into 'master'

【Issue volcano-sh#60】修复问题：对于只创建pdb没有创建podgroup的对象，使用非kube-batch调度器会导致kube-batch panic

单号:  无

特性/模块名称: kube-batch

修改原因:

1. 如题，详情见issue
![image](/uploads/c8fd4f635155aae5f782e9a566f11b0a/image.png)
![image](/uploads/7c5ebdb529375743add2e82355c35a36/image.png)
![image](/uploads/20c86e680c7ba77d9ee7e2c610699cc4/image.png)

修改内容：

1. 增加nil判断

自验情况 自验通过
验证yaml [kubeflow-mpi.yaml](/uploads/952fa8dfab1ba26bd8d8560c8da1992c/kubeflow-mpi.yaml)

Issues info:
Issue ID: 60
Title: 对于只创建pdb没有创建podgroup的对象，使用非kube-batch调度器会导致kube-batch panic
Issue url: CBU-PaaS/Community/volcano/volcano#60


See merge request CBU-PaaS/Community/volcano/volcano!99

pkg/scheduler/framework/session.go

@@ -364,6 +364,10 @@ func (ssn *Session) UpdateJobCondition(jobInfo *api.JobInfo, cond *v1alpha1.PodG
 		return fmt.Errorf("failed to find job <%s/%s>", jobInfo.Namespace, jobInfo.Name)
 	}
 
+	if job.PodGroup == nil {
+		return nil
+	}
+
 	index := -1
 	for i, c := range job.PodGroup.Status.Conditions {
 		if c.Type == cond.Type {