Return empty suffix for invalid slots am: a6759d5d am: 2dba4ac8 am:...

Return empty suffix for invalid slots am: a6759d5d am: 2dba4ac8 am: 284508d0 am: 1016c8a7 am: 4ebf7ae9

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



Change-Id: I199b772bee6194d58b02c78f0d24881ff9c90741
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>