fix 'node show' and 'shard explain' crashes (#86)

pkg/es/node.go

@@ -113,13 +113,19 @@ func NodeShow(conf *cfg.Config, nodename string) error {
 		}
 
 		k8snode := info.Attributes["k8s_node_name"]
+		rank := "none"
+
+		adsel, exists := stat.AdaptiveSelection[id]
+		if exists {
+			rank = *adsel.Rank
+		}
 
 		table.Entries = [][]any{
 			{"Id", id},
 			{"Name", nodename},
 			{"Kubernetes node", k8snode},
 			{"Ip address", info.Ip},
-			{"Node rank", *stat.AdaptiveSelection[id].Rank},
+			{"Node rank", rank},
 			{"JVM", info.Jvm.VmName + " " + info.Jvm.Version},
 			{"JVM Started", time.UnixMilli(info.Jvm.StartTimeInMillis)},
 			{"OS", info.Os.PrettyName + " " + info.Os.Version},