Merge "SystemCertificateSource: Mitigate NPE when checking updateable certs directory" into main am: b7e715d8d9

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/3165417

Change-Id: Ibea0d8e830fc22fd1312b5413f93d22a188b141c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>