[core] fix concurrency issues

* initialize first line of output earlier (before modules are
  initialized, so that module/thread output cannot interfere)
* make sure that update and draw are protected against concurrent access

bumblebee-status

@@ -75,6 +75,8 @@ def handle_events(config, update_lock):
 
 
 def main():
+    global started
+
     config = core.config.Config(sys.argv[1:])
     level = logging.DEBUG if config.debug() else logging.ERROR
     if config.logfile():
@@ -97,6 +99,8 @@ def main():
     core.input.register(None, core.input.WHEEL_UP, "i3-msg workspace prev_on_output")
     core.input.register(None, core.input.WHEEL_DOWN, "i3-msg workspace next_on_output")
 
+    core.event.trigger("start")
+
     update_lock = threading.Lock()
     event_thread = threading.Thread(target=handle_events, args=(config, update_lock, ))
     event_thread.daemon = True
@@ -127,7 +131,6 @@ def main():
     if util.format.asbool(config.get("engine.collapsible", True)) == True:
         core.input.register(None, core.input.MIDDLE_MOUSE, output.toggle_minimize)
 
-    core.event.trigger("start")
     started = True
     signal.signal(10, sig_USR1_handler)
     while True: