fix nil pointer panic for monitor

Signed-off-by: Ye Sijun <junnplus@gmail.com>

runtime/restart/monitor/monitor.go

@@ -214,22 +214,31 @@ func (m *monitor) monitor(ctx context.Context) ([]change, error) {
 	}
 	var changes []change
 	for _, c := range containers {
+		var (
+			task   containerd.Task
+			status containerd.Status
+			err    error
+		)
 		labels, err := c.Labels(ctx)
 		if err != nil {
 			return nil, err
 		}
 		desiredStatus := containerd.ProcessStatus(labels[restart.StatusLabel])
-		task, err := c.Task(ctx, nil)
+		if task, err = c.Task(ctx, nil); err == nil {
-		if err != nil && desiredStatus == containerd.Stopped {
+			if status, err = task.Status(ctx); err == nil {
-			continue
-		}
-		status, err := task.Status(ctx)
-		if err != nil && desiredStatus == containerd.Stopped {
-			continue
-		}
 				if desiredStatus == status.Status {
 					continue
 				}
+			}
+		}
+
+		// Task or Status return error, only desired to stop
+		if err != nil {
+			logrus.WithError(err).Error("monitor")
+			if desiredStatus != containerd.Stopped {
+				continue
+			}
+		}
 
 		switch desiredStatus {
 		case containerd.Running: