Upgrade zopfli to 831773bc28e318b91a3255fa12c9fcde1606058b am: a7aca0225b am: eb419370f4 am: 23e37b1188

Original change: https://android-review.googlesource.com/c/platform/external/zopfli/+/1736801

Change-Id: Iac41f3f015a7fe51e9af3cfdf1a135b3f0bde6a8