[BUG] http: fix possible incorrect forwarded wrapping chunk size

[BUG] http: fix possible incorrect forwarded wrapping chunk size

It seems like if a response message is chunked and the chunk size wraps
at the end of the buffer and the crlf sequence is incomplete, then we
can forward a wrong chunk size due to incorrect handling of the wrapped
size. It seems extremely unlikely to occur on real traffic (no reason to
have half of the CRLF after a chunk) but nothing prevents it from being
possible.

This fix must be backported to 1.4.