Style Book: Fix crash when previewing variations for blocks without examples

[SainathPoojary]

What?

Closes #79130

Adds a protective guard to applyBlockVariationsToExamples to prevent a TypeError crash when attempting to apply style variations to an undefined list of examples.

Why?

When opening the style variation detail screen for a block that does not have standalone Style Book examples (like core/column), the editor crashes.

How?

Added an early return inside applyBlockVariationsToExamples (in packages/editor/src/components/style-book/index.js) to check if ( ! variation || ! examples ). If examples evaluates to undefined, it safely returns early without calling .map(). This prevents the crash and allows the UI to gracefully render an empty/fallback preview state instead.

Testing Instructions

1. Go to Appearance > Editor to open the Site Editor.
2. Open the Styles panel (the half-black/half-white circle icon).
3. Click the Eye icon at the top right of the Styles sidebar to toggle the Style Book ON.
4. Go to Blocks and search for the Column block.
5. Click on the Column block, then click on any of its listed style variations (e.g., "Style 1").
6. Verify that the editor does not crash and the console is free of TypeError: Cannot read properties of undefined (reading 'map') errors.

Screenshots or screencast

Before	After

[im3dabasia]

The changes look good to me, Let me know once the PR is ready for review!

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Co-authored-by: SainathPoojary <[email protected]>
Co-authored-by: t-hamano <[email protected]>
Co-authored-by: im3dabasia <[email protected]>
Co-authored-by: aaronjorbin <[email protected]>

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[SainathPoojary]

Thanks @im3dabasia! This PR is ready for review from my side.

[t-hamano]

Thank for the PR.

if ( ! variation || ! examples ) {
	return examples;
}

This logic seems strange. Why would it return an example when there is no example provided?

This seems to be an issue that should be addressed upstream.

if ( blockVariation && filteredExamples?.examples?.length ) {
	return {
		examples: applyBlockVariationsToExamples(
			filteredExamples.examples,
			blockVariation
		),
	};
}

The advantage of this approach is that the stylebook does not become empty.

[SainathPoojary]

Thanks for the review and the great suggestion @t-hamano! I've moved the check upstream to displayedExamples as you suggested. Just pushed the update!

[t-hamano]

LGTM!