Fix exposing private messages files through attachments with a content URI. am: 0d5452146c am: f5c73b1923 am: 83d5883687 am: 5b110f95e9

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

Change-Id: I29293e85cf9f1d845be9a035f1ab9eefc4d5812c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>