fix(useIntersectionObserver): targets length check

[schelmo]

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⚠️ Slowing down new functions

Warning: Slowing down new functions

As the VueUse audience continues to grow, we have been inundated with an overwhelming number of feature requests and pull requests. As a result, maintaining the project has become increasingly challenging and has stretched our capacity to its limits. As such, in the near future, we may need to slow down our acceptance of new features and prioritize the stability and quality of existing functions. Please note that new features for VueUse may not be accepted at this time. If you have any new ideas, we suggest that you first incorporate them into your own codebase, iterate on them to suit your needs, and assess their generalizability. If you strongly believe that your ideas are beneficial to the community, you may submit a pull request along with your use cases, and we would be happy to review and discuss them. Thank you for your understanding.

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Description

makes useIntersectionObserver actually work (and also useElementVisibility)

Additional context

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🤖 Generated by Copilot at fa20a33

Fixed a bug in useIntersectionObserver that caused errors when no targets were provided. Improved the performance and reliability of the function.

🤖 Generated by Copilot at fa20a33

• Fix early return condition in useIntersectionObserver to avoid unnecessary or invalid calls to observer.observe (link)