olm: Also initialize all fields when decoding Olm messages.

As a precaution.
2 jobs for master in 9 minutes and 19 seconds (queued for 6 seconds)
Child pipeline (parent)
Status Name Job ID Coverage
  Build
passed build:android:aar #14072
docker

00:05:29

 
  Test
passed test:android:aar #14075
docker

00:03:49