cmd/cue: fix help cmd incorrect behavior

This fixes the issue of incorrect behavior when requesting help for an unknown command in the CUE CLI.
1. Modified the  function to handle unknown commands correctly.
2. When an unknown  and  commands are entered, an error message is displayed and the program exits with a non-zero status code.
3. This ensures that the CLI behaves as expected and provides useful feedback to the user when an unknown command is entered.
Fixes #2560

Signed-off-by: nnnkkk7 <kurodanaoki0711pana@gmail.com>

cmd/cue/cmd/help.go

@@ -15,6 +15,9 @@
 package cmd
 
 import (
+	"os"
+	"strings"
+
 	"github.com/spf13/cobra"
 )
 
@@ -49,18 +52,19 @@ Simply type ` + c.Name() + ` help [path to command] for full details.`,
 				}
 
 				tools, err := buildTools(c, pkgArgs)
-				if err == nil {
-					addCustomCommands(c, cmd, commandSection, tools)
-					// For the sake of `cue help cmd mycmd`, find the command again.
-					cmd, _, e = c.Root().Find(args)
+				if err != nil {
+					c.PrintErrf("Unknown help cmd command: %#q\n", strings.Join(args[1:], " "))
+					os.Exit(1)
 				}
+				addCustomCommands(c, cmd, commandSection, tools)
+				// For the sake of `cue help cmd mycmd`, find the command again.
+				cmd, _, e = c.Root().Find(args)
 			}
-			if cmd == nil || e != nil {
-				c.Printf("Unknown help topic %#q\n", args)
-				cobra.CheckErr(c.Root().Usage())
-			} else {
-				cobra.CheckErr(cmd.Help())
+			if cmd == nil || e != nil || (len(args) > 0 && args[0] != "cmd") {
+				c.PrintErrf("Unknown help command: %#q\n", strings.Join(args, " "))
+				os.Exit(1)
 			}
+			cobra.CheckErr(cmd.Help())
 		},
 	}
 	return cmd