Return empty suffix for invalid slots am: a6759d5d66 am: 2dba4ac8b4

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2166409

Change-Id: Id5a45519a52e90cf9ff936ba50c1678dcb93cd2a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>