Fix exposing private messages files through attachments with a content URI. am: 0d5452146c am: f5c73b1923 am: a4838ac96e am: 2ffa017167

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Messaging/+/23089831

Change-Id: Ib854c5b9807e0ad4552e6b330a4f8441135b8741
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>