fix(messages): nullish value checks in message content generation

[vinikjkkj]

Will be ignored:

await sock.sendMessage(jid, { text: undefined })

Will be accepted:

await sock.sendMessage(jid, { text: 'hello' })

This PR is a rework of #1591

[whiskeysockets-bot]

Thanks for opening this pull request and contributing to the project!

The next step is for the maintainers to review your changes. If everything looks good, it will be approved and merged into the main branch.

In the meantime, anyone in the community is encouraged to test this pull request and provide feedback.

✅ How to confirm it works

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Tested and working ✅

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📦 To test this PR locally:

# NPM
npm install @whiskeysockets/baileys@WhiskeySockets/Baileys#fix-nullish-values

# Yarn (v2+)
yarn add @whiskeysockets/baileys@WhiskeySockets/Baileys#fix-nullish-values

# PNPM
pnpm add @whiskeysockets/baileys@WhiskeySockets/Baileys#fix-nullish-values

If you encounter any issues or have feedback, feel free to comment as well.

[Salientekill]

Thank you for your work.

[FightFarewellFearless]

Thank you!

[purpshell]

Thank you for your work and thanks to @FightFarewellFearless for the original implementation. Love to see it

[github-actions]

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