refactor(ValidateRequestBody): reduce cyclomatic complexity and indent

[nickajacks1]

Use the early-out pattern to reduce code complexity.
None of the existing logic should have changed, and all tests pass.

@daveshanley Can you fact check me at line 40? At this point, are there any errors that could occur here?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (affb03c) 100.00% compared to head (ada5f58) 100.00%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #29   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           18        18           
  Lines         1055      1071   +16     
=========================================
+ Hits          1055      1071   +16     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
requests/validate_body.go	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[daveshanley]

A missing content type, I mean there is nothing to do, there is no work to perform, there is no way to know what to validate.

As soon as the coverage is back at 100%, I can merge this. I can't let coverage drop on this codebase, the tests are the guarantee it is as robust as we can make it.

[nickajacks1]

As soon as the coverage is back at 100%, I can merge this

Sure, I will take a crack at it.

From a branch coverage perspective though, the coverage remains identical since there is no logical change from the existing code. It's highly likely that there are more of these uncovered branches elsewhere in the code - for example, see validate_request.go. It also has a highly indented function that may or may not be missing test cases.
Going beyond line coverage may be effective in boosting the robustness of this library.

[nickajacks1]

A missing content type, I mean there is nothing to do, there is no work to perform, there is no way to know what to validate.

Instantly passing validation is probably wrong as it might let an invalid body through to later handlers. I'm thinking it would be better to return errors.RequestContentTypeNotFound

[nickajacks1]

By the way, I created TestValidateBody_MediaTypeHasNullSchema to reach 100% coverage, but it's technically testing an invalid openapi doc. A media type object must have a schema field (which can itself be empty, but then that doesn't cover the Schema == nil check).