Fix out of bounds in libincfs-test. am: 20698192b9 am: 57722469e4 am: 98f21490fd

Original change: https://android-review.googlesource.com/c/platform/system/incremental_delivery/+/2051988

Change-Id: I9ed9bff89a1b03ee022c3bef560eddcdebb5d539
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>