allow preloading modules without referencing by filename

[madflow]

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

• Tries to fix fastify -r does not behave like node -r #357 by leaving the current logic intact
• First checks if the provided module name is an existing file - if not - just use require(id)

[mcollina]

lgtm

[mcollina]

lgtm