[CVE-2022-43680] Fix overeager DTD destruction (fixes #649) am: 6944d3ebed am: 7c4bee3669 am: d220ca60bd am: 619b9592e6 am: 93d737c088 am: 6fa479c5eb am: 9862b0a175 am: 4a839dce62

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/expat/+/20497949

Change-Id: I8dc71c88e036bff453f6bcb166871a01de973934
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>