Bug 1123507: Prevent out of bound memory access. r=edwin

--HG--
extra : rebase_source : 48c8a833b0b394d0c35754b2311f54e8bf8c5b66

media/libstagefright/binding/Box.cpp

@@ -48,8 +48,8 @@ Box::Box(BoxContext* aContext, uint64_t aOffset, const Box* aParent)
     if ((mParent && !mParent->mRange.Contains(bigLengthRange)) ||
         !byteRange->Contains(bigLengthRange) ||
         !mContext->mSource->CachedReadAt(aOffset, bigLength,
-                                         sizeof(bigLengthRange), &bytes) ||
-        bytes != sizeof(bigLengthRange)) {
+                                         sizeof(bigLength), &bytes) ||
+        bytes != sizeof(bigLength)) {
       return;
     }
     size = BigEndian::readUint64(bigLength);