Check whether there are any cursor metadata before we try to validate and use them, otherwise we might crash on this. Bug: webrtc:13429 Change-Id: I365da59a189b6b974cebafc94fec49d5b942efae Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/255601 Reviewed-by: Alexander Cooper <alcooper@chromium.org> Commit-Queue: Alexander Cooper <alcooper@chromium.org> Cr-Commit-Position: refs/heads/main@{#36240}