fix: add missing "return" statements after errors

[brianphillips]

Description

When a route function returns an error early on in the function body (i.e. validating the presence of a field), it's important to not continue executing the function to ensure a) no undesired code is executed, and b) to avoid trying to emit headers multiple times.

Issue number: n/a

Type of change

• New feature (non-breaking change which adds functionality)
• Fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• Changes generate no new warnings
• PR title follows conventional commit semantics

If this is a breaking change 👇

• I have documented the migration process
• I have implemented necessary warnings (if it can live side by side)

Acknowledgement

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[t1agob]

Thanks for the contribution @brianphillips! This is now tested an approved.