ANDROID: Skip pre-push hook if it doesn't exist. am: 16fb9454bb

Original change: https://android-review.googlesource.com/c/platform/external/drm_hwcomposer/+/3308060

Change-Id: I3f9b136ad3bb5e737d38c590ed7a070f00d8a601
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>