[automerger skipped] Prevent integer overflow in copyString am: e25c840375 am: f2b297c3bd -s ours am: b3aad8888b -s ours am: fb2a7f1ff8 -s ours am: 9082284b62 -s ours

am skip reason: skipped by user enh

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/expat/+/18566079

Change-Id: Ic32af738899fcb32c7207ec9229b640e3add35d2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>