String16::remove - avoid overflow am: 4048e49956 am: 107f18cb61 am: 9be245c3f0 am: 64fb5012b8 am: 4e27b6992b am: 26b81f59d2

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/core/+/11619802

Change-Id: Ib4704bc8a733ace56e7998b7bad5a6c5638900ad