cmd/puppeth: handle pre-set Petersburg number, save changed fork rules

cmd/puppeth/wizard_genesis.go

@@ -222,14 +222,18 @@ func (w *wizard) manageGenesis() {
 		fmt.Println()
 		fmt.Printf("Which block should Constantinople come into effect? (default = %v)\n", w.conf.Genesis.Config.ConstantinopleBlock)
 		w.conf.Genesis.Config.ConstantinopleBlock = w.readDefaultBigInt(w.conf.Genesis.Config.ConstantinopleBlock)
-
+		if w.conf.Genesis.Config.PetersburgBlock == nil {
+			w.conf.Genesis.Config.PetersburgBlock = w.conf.Genesis.Config.ConstantinopleBlock
+		}
 		fmt.Println()
-		fmt.Printf("Which block should Constantinople-Fix (remove EIP-1283) come into effect? (default = %v)\n", w.conf.Genesis.Config.ConstantinopleBlock)
-		w.conf.Genesis.Config.PetersburgBlock = w.readDefaultBigInt(w.conf.Genesis.Config.ConstantinopleBlock)
+		fmt.Printf("Which block should Constantinople-Fix (remove EIP-1283) come into effect? (default = %v)\n", w.conf.Genesis.Config.PetersburgBlock)
+		w.conf.Genesis.Config.PetersburgBlock = w.readDefaultBigInt(w.conf.Genesis.Config.PetersburgBlock)
 
 		out, _ := json.MarshalIndent(w.conf.Genesis.Config, "", "  ")
 		fmt.Printf("Chain configuration updated:\n\n%s\n", out)
 
+		w.conf.flush()
+
 	case "2":
 		// Save whatever genesis configuration we currently have
 		fmt.Println()