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

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

Change-Id: Ib8ebf64c5b03f8175fdcac5177a48b19423f093a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>