Merge "Upgrade libpng to v1.6.40" am: 27bd9cf3d0

Original change: https://android-review.googlesource.com/c/platform/external/libpng/+/2636112

Change-Id: I6e3f06caa2b136ef06deedc85a54f3839f9cf155
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>