lfb-event: Notify state change before completing async task

lfb_event_trigger_feedback_async() internally uses a GTask to handle
invocation of the user provided callback when g_task_return_*() is
called.

Currently GTask is completed first and only afterwards is the state of
the event being updated which can lead to suprising behaviour in code
like this:

static void
on_event_triggered (LfbEvent     *event,
                    GAsyncResult *res,
                    CallsRinger  *self)
{
  g_autoptr (GError) err = NULL;
  gboolean ok;

  g_return_if_fail (LFB_IS_EVENT (event));

  ok = lfb_event_trigger_feedback_finish (event, res, &err);
  if (ok) {
    LfbEventState state = lfb_event_get_state (event);
    /* do something with state */
  }
}

In this case `state` would return a stale value that's about to get
changed. Instead it would be better to *first* change the state and only
afterwards complete the GTask.

This also makes the sync and async variants consistent in terms of when
they change the event state.

Closes: #59

libfeedback/lfb-event.c

@@ -150,7 +150,6 @@ on_trigger_feedback_finished (LfbGdbusFeedback *proxy,
   LfbEvent *self = data->event;
   g_autoptr (GError) err = NULL;
   gboolean success;
-  LfbEventState state;
 
   g_return_if_fail (G_IS_TASK (task));
   g_return_if_fail (LFB_GDBUS_IS_FEEDBACK (proxy));
@@ -160,16 +159,15 @@ on_trigger_feedback_finished (LfbGdbusFeedback *proxy,
                                                              &self->id,
                                                              res,
                                                              &err);
+
+  lfb_event_set_state (self, success ? LFB_EVENT_STATE_RUNNING : LFB_EVENT_STATE_ERRORED);
   if (!success) {
     g_task_return_error (task, g_steal_pointer (&err));
-    state = LFB_EVENT_STATE_ERRORED;
   } else {
     g_task_return_boolean (task, TRUE);
-    state = LFB_EVENT_STATE_RUNNING;
     _lfb_active_add_id (self->id);
   }
 
-  lfb_event_set_state (self, state);
   g_free (data);
   g_object_unref (task);
   g_object_unref (self);