[CVE-2022-43680] Fix overeager DTD destruction (fixes #649) am: eb8f10fb1f am: 811c3ce5a3 am: 242a8a8638 am: 7b703e38f5 am: d2a7aecfea am: 0f8f85c073 am: 39ce9f2511 am: ec68b0bceb

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/expat/+/20494973

Change-Id: Ie9c62a45742a25def607c1a9cf8c92be32753b87
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>