Add Null checks in LinkToTextCoordinator before requesting canonicalUrl

Change-Id: Ia72088f9be690ec98de3efec6592449691c052ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3145180


Commit-Queue: Cheick Cisse <cheickcisse@google.com>
Reviewed-by: Gayane Petrosyan <gayane@google.com>
Reviewed-by: Sophey <sophey@chromium.org>
Cr-Commit-Position: refs/heads/main@{#919273}