Fix seek behaviour at startup and teardown of media session that hasn't been started

Nuplayer specific.

Change-Id: I7b0be52c29bdb7032414d63c503d686df7844bf6
diff --git a/media/libmediaplayerservice/nuplayer/HTTPLiveSource.cpp b/media/libmediaplayerservice/nuplayer/HTTPLiveSource.cpp
index 5a5330d..0251baf 100644
--- a/media/libmediaplayerservice/nuplayer/HTTPLiveSource.cpp
+++ b/media/libmediaplayerservice/nuplayer/HTTPLiveSource.cpp
@@ -58,8 +58,10 @@
 }
 
 NuPlayer::HTTPLiveSource::~HTTPLiveSource() {
-    mLiveSession->disconnect();
-    mLiveLooper->stop();
+    if (mLiveSession != NULL) {
+        mLiveSession->disconnect();
+        mLiveLooper->stop();
+    }
 }
 
 void NuPlayer::HTTPLiveSource::start() {