`mergeBufferGeometries` give error for empty array

• three version: 0.160
• @types/three version:
• three-stdlib version:

Problem description:

mergeBufferGeometries gives error Uncaught TypeError: Cannot read properties of undefined (reading 'index')
It is from some sloppy list access

https://github.com/pmndrs/three-stdlib/blame/45e22a1b636241147934e8bd9f22d506ccfc3cf0/src/utils/BufferGeometryUtils.ts#L27

which also exists in three.js upstream

https://github.com/mrdoob/three.js/blob/de6dd45d7e5aa58fed0fbc1dbe53def3402b39cc/examples/jsm/utils/BufferGeometryUtils.js#L109C20-L109C51

Relevant code:

Suggested solution:

I generally would return some reasonable identity object for such cases than raising sloppy errors.
Maybe null can be reasonable.

Or otherwise, it may be useful to denote the types as [BufferGeometry, ...BufferGeometry[]] instead of BufferGeometry[],
where typescript can just warn users that users should pass array with at least one element.

Start in src/utils/BufferGeometryUtils.ts at mergeBufferGeometries and reproduce the empty-array call that triggers the undefined-index TypeError. Compare the linked upstream three.js implementation, settle the intended empty-input behavior, and ensure the runtime behavior and TypeScript signature consistently communicate that result.