st/oxr: Fix conformance issue in begin session.

4 jobs for master in 58 seconds (queued for 1 second)
Status Job ID Name Coverage
  Container Prep
passed #258698
arch:container_prep

00:00:20

passed #258697
debian:container_prep

00:00:16

 
  Build
passed #258700
arch:build-cmake

00:00:22

passed #258699
debian:build-cmake

00:00:24