Fix initialization

Change-Id: I17a82a4555d8b577e03c0ede41e55ba881fe3d02
diff --git a/framesequence/jni/FrameSequence_webp.h b/framesequence/jni/FrameSequence_webp.h
index 94dcc3b..c43c1e7 100644
--- a/framesequence/jni/FrameSequence_webp.h
+++ b/framesequence/jni/FrameSequence_webp.h
@@ -70,7 +70,7 @@
     uint32_t mFormatFlags;
     // mIsKeyFrame[i] is true if ith canvas can be constructed without decoding any prior frames.
     bool* mIsKeyFrame;
-    jobject mRawByteBuffer;
+    jobject mRawByteBuffer = nullptr;
 };
 
 // Produces frames of a possibly-animated WebP file for display.