fix: bypass Content-Type validation when request has no body

[sjorobekov]

Description:

What changed?

Updated the withContract function to only enforce Content-Type header validation if the incoming request actually contains a payload.

Why?

Previously, if a route contract defined a body schema but the client sent a request without a body (and thus no Content-Type header), the function would throw an Unsupported content-type error. This fix ensures that requests without a body bypass the strict Content-Type check and correctly fall through to the standard schema validation, which will properly handle the missing body.

Details:

• Added a hasBody check using transfer-encoding and content-length headers.
• Wrapped the Content-Type validation logic inside the hasBody condition.
• Added a test case to verify that empty body requests bypass the content-type check and return standard validation errors.