Use postValuse to send event

To avoid send event in background thread.

src/main/java/com/kdanmobile/reader/event/EventManager.kt

@@ -12,9 +12,9 @@ class EventManager<T> : EventBroadcaster<T> {
 
     @Synchronized
     fun send(event: T) {
-        if (eventLiveDataImp.value == null) {
+        if (currentEvent == null) {
             currentEvent = event
-            eventLiveDataImp.value = currentEvent
+            eventLiveDataImp.postValue(currentEvent)
         } else {
             queue.offer(event)
         }