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

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

Change-Id: Ida74ec2de652b8e4fcb874a111852f655ba64cfe
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>