threadnetwork: Avoid execute command if service does not exist am: 0afad08ea2 am: bac748d16d

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/3343649

Change-Id: If7658b14fd9fff4e57b6ea4654dd883e6160207e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>