HttpMessageConverterExtractor uses MessageBodyClientHttpResponseWrapper
which may read the first byte of the response stream to check if there
is content. After that it is necessary to use the wrapper to get the
full body.
This commit ensures that when UnknownContentTypeException is raised
it gets the body through the wrapper, or otherwise the first byte is
missed if the InputStream is not markable.
Closes gh-27374
63ffa710d6