MPEG4Writer: fix unintiialized member variables

bug: 20858729
Change-Id: Iccd62dca311fa66cb52ef53ed703719ddcf92cc8
diff --git a/media/libstagefright/MPEG4Writer.cpp b/media/libstagefright/MPEG4Writer.cpp
index 3bc22f2..95f361e 100644
--- a/media/libstagefright/MPEG4Writer.cpp
+++ b/media/libstagefright/MPEG4Writer.cpp
@@ -369,9 +369,16 @@
       mWriterThreadStarted(false),
       mOffset(0),
       mMdatOffset(0),
+      mMoovBoxBuffer(NULL),
+      mMoovBoxBufferOffset(0),
+      mWriteMoovBoxToMemory(false),
+      mFreeBoxOffset(0),
+      mStreamableFile(false),
       mEstimatedMoovBoxSize(0),
       mMoovExtraSize(0),
       mInterleaveDurationUs(1000000),
+      mTimeScale(-1),
+      mStartTimestampUs(-1ll),
       mLatitudex10000(0),
       mLongitudex10000(0),
       mAreGeoTagsAvailable(false),