Merge "Upgrade libpng to v1.6.40" am: 27bd9cf3d0 am: 6f2b0d3a5f am: edfff8897e am: b936c177bb

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

Change-Id: I07777ef3553a1014f75f4be9e93b634721117092
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>