Cleanup createTrack error handling

Similar to cleanup done earlier for openRecord in this CL:
    > Change-Id: I84897dd7d30b370640b54e928f230604b873cb68

Bug: 10888816
Change-Id: I804a47f898e0319a60a9bd58906bbb037e45cc25
diff --git a/media/libmedia/AudioTrack.cpp b/media/libmedia/AudioTrack.cpp
index d5e3e67..a113f77 100644
--- a/media/libmedia/AudioTrack.cpp
+++ b/media/libmedia/AudioTrack.cpp
@@ -1004,6 +1004,11 @@
         ALOGE("Could not get control block");
         return NO_INIT;
     }
+    void *iMemPointer = iMem->pointer();
+    if (iMemPointer == NULL) {
+        ALOGE("Could not get control block pointer");
+        return NO_INIT;
+    }
     // invariant that mAudioTrack != 0 is true only after set() returns successfully
     if (mAudioTrack != 0) {
         mAudioTrack->asBinder()->unlinkToDeath(mDeathNotifier, this);
@@ -1011,7 +1016,7 @@
     }
     mAudioTrack = track;
     mCblkMemory = iMem;
-    audio_track_cblk_t* cblk = static_cast<audio_track_cblk_t*>(iMem->pointer());
+    audio_track_cblk_t* cblk = static_cast<audio_track_cblk_t*>(iMemPointer);
     mCblk = cblk;
     size_t temp = cblk->frameCount_;
     if (temp < frameCount || (frameCount == 0 && temp == 0)) {