Return empty suffix for invalid slots am: a6759d5d66

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

Change-Id: I1765260c7031f2ef4daa5ea9ac1f4d576da7345d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>