HTTP/2: client_header_timeout before first request (ticket #2142). With this change, behaviour of HTTP/2 becomes even closer to HTTP/1.x, and client_header_timeout instead of keepalive_timeout is used before the first request is received. This fixes HTTP/2 connections being closed even before the first request if "keepalive_timeout 0;" was used in the configuration; the problem appeared in f790816a0e87 (1.19.7).