cmd/geth: make dumpgenesis load genesis datadir if it exists (#25135)

`geth dumpgenesis` currently does not respect the content of the data directory. Instead, it outputs the genesis block created by command-line flags. This PR fixes it to read the genesis from the database, if the database already exists.


Co-authored-by: Martin Holst Swende <martin@swende.se>

cmd/utils/flags.go

@@ -988,9 +988,7 @@ var (
 		KilnFlag,
 	}
 	// NetworkFlags is the flag group of all built-in supported networks.
-	NetworkFlags = append([]cli.Flag{
-		MainnetFlag,
-	}, TestnetFlags...)
+	NetworkFlags = append([]cli.Flag{MainnetFlag}, TestnetFlags...)
 
 	// DatabasePathFlags is the flag group of all database path flags.
 	DatabasePathFlags = []cli.Flag{
@@ -2140,6 +2138,16 @@ func MakeChainDatabase(ctx *cli.Context, stack *node.Node, readonly bool) ethdb.
 	return chainDb
 }
 
+func IsNetworkPreset(ctx *cli.Context) bool {
+	for _, flag := range NetworkFlags {
+		bFlag, _ := flag.(*cli.BoolFlag)
+		if ctx.IsSet(bFlag.Name) {
+			return true
+		}
+	}
+	return false
+}
+
 func MakeGenesis(ctx *cli.Context) *core.Genesis {
 	var genesis *core.Genesis
 	switch {