[core] alloc optim reading file, sending chunked
[core] alloc optim reading file, sending chunked

avoid potential double-copy due to not enough space for final '\0'
in http_chunk_append_read_fd_range() if read size is exactly multiple
of 8k and sending chunked response

lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4