Check size of grantors before indexing into the vec am: 2b686fcd97 am: ca82973033

Original change: https://android-review.googlesource.com/c/platform/system/libhidl/+/2113745

Change-Id: Id29ec2a29622d304c353734be07c921cb748be02
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>