Protect STHelper from calls after detach am: 14de6500 am: ba5164c9 am: fe4e5dfa

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22477697



Change-Id: I5c8a269f913a24cd7d1e4cc8c78cfa60d336f0c2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>