cmd/bootnode: fix exit behavior with -genkey (#20110)

cmd/bootnode/main.go

@@ -70,7 +70,9 @@ func main() {
 		if err = crypto.SaveECDSA(*genKey, nodeKey); err != nil {
 			utils.Fatalf("%v", err)
 		}
-		return
+		if !*writeAddr {
+			return
+		}
 	case *nodeKeyFile == "" && *nodeKeyHex == "":
 		utils.Fatalf("Use -nodekey or -nodekeyhex to specify a private key")
 	case *nodeKeyFile != "" && *nodeKeyHex != "":