set_payload_max_length(0) is documented to disable the limit, but the
readers for a chunked body and for a body delimited by the connection
closing compared the size against the limit without checking for 0.
A server configured that way answered a chunked request with 413, and
a client failed to read a chunked or unframed response. A body with
Content-Length was already unlimited.
Give both readers the same `payload_max_length > 0` guard the other
payload checks use.
84ff13ec47
