fix: delete unreachable branch

[zekth]

Was stumbling upon improving code coverage and this branch is unreachable:
https://github.com/fastify/fastify/blob/master/lib/request.js#L33
Because of this condition:
https://github.com/fastify/fastify/blob/master/lib/request.js#L37

So it makes sense to replace .compile(tp || [] ) with compile(tp)

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm

[github-actions]

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