Resolve cross-user image exploit for conference status hints

Ensure that status hint image icon is validated for cross-user exploits.
Currently, there is no check for this so a conference call can display
an image from another user, exposing a vulnerability.

Bug: 329058967
Test: Manual with POC
Change-Id: Ib9d701398d25d021cdb9abacbaa5b175f62bee1d