[mod_sockproxy] reset http vers, avoid rare crash (fixes #3152)

(thx ultimator)

x-ref:
  "Random Segfaults with version 1.4.64 w/ mod_sockproxy and ALPN h2"
  https://redmine.lighttpd.net/issues/3152

src/mod_sockproxy.c

@@ -163,6 +163,7 @@ static handler_t mod_sockproxy_connection_accept(connection *con, void *p_d) {
 		hctx->create_env = sockproxy_create_env_connect;
 		hctx->response = chunk_buffer_acquire();
 		r->http_status = -1; /*(skip HTTP processing)*/
+		r->http_version = HTTP_VERSION_UNSET;
 	}
 
 	return HANDLER_GO_ON;