fix(select): guard against null ref in typeahead focus

[Tourniercy]

Description

Fixes #3597

Adds a null check on nextItem.ref.current before calling .focus() in the typeahead search handler within SelectContentImpl.

When using the Select component on mobile browsers (observed on Android Chrome), the DOM element referenced by nextItem.ref.current can be null if the element hasn't mounted yet or has been unmounted due to timing issues.

This causes an unhandled TypeError: Cannot read properties of null (reading 'focus').

[changeset-bot]

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Latest commit: 1299a55

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