Handles optional request bodies

[emilien-puget]

As i just discovered, request bodies are optional by default.
see https://spec.openapis.org/oas/v3.1.0#fixed-fields-10 or https://swagger.io/docs/specification/describing-request-body/
this dear library doesn't handle such cases

libopenapi-validator/requests/validate_body.go

Line 41 in 688b7a2

contentType := request.Header.Get(helpers.ContentTypeHeader)

as we can see above, if an operation has a request body, we will require to have a content type set, however that request body could be not required which means that a content type should not be required.

i haven't go any further in my investigation, maybe the underlying lib is already capable of handling such cases, any if we agree that this is not an expected behavior i can propose a fix in a few hours/days.

[daveshanley]

Yeah, I agree if required is set to false (which as you pointed out, is the default), then the library should be able to handle it.

[emilien-puget]

here it is #71