Merge "Upgrade libpng to v1.6.39" am: cb9e209cab am: c05ebac440

Original change: https://android-review.googlesource.com/c/platform/external/libpng/+/2435872

Change-Id: I1f08558da6b79ca77bcc65ab0552010aec33166f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>