Add checks to avoid null pointer exceptions when checking viewport-fit

Bug: 329990047
Change-Id: If0d3110ce8bb049e50a7a2ad1e434a31557eb8f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5399127


Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Commit-Queue: Charles Hager <clhager@google.com>
Reviewed-by: Charlie Reis <creis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280035}