Bug fix : enqueue one next subtitle for each subtitle.

o Do not enqueue another subtitle when notifying a null message.
related-to-bug: 6401574

Change-Id: I366e643ffa1601c11a12e46fcf7c00a469c77448
diff --git a/media/libstagefright/timedtext/TimedTextPlayer.cpp b/media/libstagefright/timedtext/TimedTextPlayer.cpp
index dc5f6b8..f855d90 100644
--- a/media/libstagefright/timedtext/TimedTextPlayer.cpp
+++ b/media/libstagefright/timedtext/TimedTextPlayer.cpp
@@ -112,15 +112,14 @@
               break;
             }
             sp<RefBase> obj;
-            msg->findObject("subtitle", &obj);
-            if (obj != NULL) {
+            if (msg->findObject("subtitle", &obj)) {
                 sp<ParcelEvent> parcelEvent;
                 parcelEvent = static_cast<ParcelEvent*>(obj.get());
                 notifyListener(&(parcelEvent->parcel));
+                doRead();
             } else {
                 notifyListener();
             }
-            doRead();
             break;
         }
         case kWhatSetSource: {