Since the changes introduced in SPR-12778, some `@RequestBody` args
would not be properly processed in some cases:
* requests with an empty body
* no Content-Type header defined
This typically happens when GET requests are mapped on a handler dealing
with POST requests and HTTP bodies.
This change makes sure that the `RequestResponseBodyMethodProcessor` is
only involved for requests that:
* have a Content-Type defined
* OR are HTTP requests eligible for an HTTP body (PUT, POST, PATCH)
Issue: SPR-13176
Fixesspring-projects/spring-boot#3313
244c95b076