bar: call refresh() after all modules have been loaded

This also means that modules do *not* have to call bar->refresh() just
before/after calling module_signal_ready().

As long as the module's initial state has been correctly/completely
set up before it calls module_signal_ready(), the module *only* has to
call bar->refresh() when it's state changes.

bar.c

@@ -171,6 +171,8 @@ expose(const struct bar *_bar)
     }
 }
 
+static void refresh(const struct bar *bar);
+
 static int
 run(struct bar_run_context *run_ctx)
 {
@@ -428,6 +430,8 @@ run(struct bar_run_context *run_ctx)
     close(ready_fd);
     LOG_DBG("all modules started");
 
+    refresh(_bar);
+
     int fd = xcb_get_file_descriptor(bar->conn);
 
     while (true) {