ExifInterface: Set mPosition in AssetStream with proper values

Bug: 28649955
Change-Id: I25ab833f54e4ee853d3b89af513b4ecd7dc02df9
diff --git a/media/jni/android_media_Utils.cpp b/media/jni/android_media_Utils.cpp
index 62685c9..359ebad 100644
--- a/media/jni/android_media_Utils.cpp
+++ b/media/jni/android_media_Utils.cpp
@@ -31,7 +31,7 @@
 namespace android {
 
 AssetStream::AssetStream(SkStream* stream)
-    : mStream(stream) {
+    : mStream(stream), mPosition(0) {
 }
 
 AssetStream::~AssetStream() {
@@ -48,7 +48,7 @@
 
     // Read bytes.
     size_t size = mStream->read((void*)data, length);
-    mPosition += size;
+    mPosition = offset + size;
 
     return size == length ? piex::Error::kOk : piex::Error::kFail;
 }