Send TMATE_READY message when the config files are done loading

This fixes bug where webhooks are not registering correctly, leading to
a disconnect and reconnect.

server.c

@@ -205,10 +205,6 @@ server_start(struct event_base *base, int lockfd, char *lockfile)
 
 	status_prompt_load_history();
 
-#ifdef TMATE
-	tmate_write_ready();
-#endif
-
 	server_add_accept(0);
 
 	proc_loop(server_proc, server_loop);

tmate-session.c

@@ -138,6 +138,7 @@ void tmate_session_start(void)
 	 * - While we are parsing the config file, we need to be able to
 	 *   serialize it, and so we need a worker encoder.
 	 */
+	tmate_write_ready();
 	lookup_and_connect();
 }