DrmHalTest: null check for skipped test am: 9049fc93a8

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2417394

Change-Id: Ibcc9f17acb7b2d43b24496c07a5ad2992b659977
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>