[core] debug server.log-request-header-on-error

enable server.log-request-header-on-error when either
server.log-request-handling or server.log-request-header
are enabled in the global scope.

server.log-request-header-on-error is a global directive since it must
be set prior to parsing of request, and errors parsing request might
otherwise occur before lighttpd config conditions are parsed and set
(i.e. based on the parsed request headers)

x-ref:
  "Log error if Host name is illegal (e.g. contains an underscore)"
  https://redmine.lighttpd.net/issues/2885

src/configfile.c

@@ -508,6 +508,9 @@ static int config_insert(server *srv) {
 		                                      |HTTP_PARSEOPT_HOST_NORMALIZE):0)
 		  |(srv->srvconf.http_host_normalize ?(HTTP_PARSEOPT_HOST_NORMALIZE):0);
 		s->http_parseopts |= srv->srvconf.http_url_normalize;
+
+		if (s->log_request_handling || s->log_request_header)
+			srv->srvconf.log_request_header_on_error = 1;
 	}
 
 	if (0 != stat_cache_choose_engine(srv, stat_cache_string)) {