fix: do not throw error when no subcommand specified but main has run

[sxzz]

🔗 Linked issue

closes #35

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Fixes emitting an error when there's main command and sub-commands

 ERROR  Unknown command undefined

Reproduction:

const validate = defineCommand({
  run() {
    console.log('run')
  },
})

const main = defineCommand({
  meta: {
    name,
    version,
    description,
  },
  subCommands: {
    validate,
  },
  run() {
    console.log('run main')
  },
})

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[pi0]

Thanks for detailed PR and sorry took long to review ❤️

[pi0]

I am thinking as a relevant fix, only run cmd.run when there is no sub-command wdyt?