Mail: disabled handling of headers without a colon in auth_http

Mail: disabled handling of headers without a colon in auth_http

Header names not followed by a colon and a value in an auth_http server
response were accepted as headers with an empty value, similarly to
ngx_http_parse_header_line().  With this change, such headers are
rejected with the "sent invalid header in response" error, and the
client gets the internal server error reply.

The problem appeared in 5192b3651 (0.1.38).