am aafda1c6: (-s ours) am df9ea768: am dcf0db2c: (-s ours) Backport fix of buffer overwrite in png_build_index. DO NOT MERGE

* commit 'aafda1c6ff0457d717f6c89d42010a6beccdf1cb':
  Backport fix of buffer overwrite in png_build_index. DO NOT MERGE