Proper handling of GET request with body in case of chained redirections

 
QTBUG-112871 has introduced GET requests with body. However, in case of chained redirections the current implementation is incorrect.

For example, in case of a 301 (moved permanently) we are clearing both the body and the headers. If this is followed by a 308 (permanent redirect) the headers are reconstructed from the original request, but the body is not. This is wrong, the headers and the body should be kept in sync.