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}