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

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

Change-Id: Ic8fd2985753a8bb1955adaca127c0304527294ac
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>