Revert "Fix buffer overwrite in png_build_index" DO NOT MERGE

This reverts commit 6b38063822f28d9a46df5e5701d585d387e03f0e.

This change is broken for kitkat (based on libpng 1.2.x) but valid
on lmp-dev (based on libpng 1.6.x) and later.

bug: 19507636
1 file changed