PageInfo: Avoid crash in sentiment service

Avoid crash when PageInfoClosed() is called twice in a row.

Bug: 41496567
Change-Id: I479cf1913284e640216ad72715fabc450d7fd93a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5615331


Commit-Queue: Mohamad Arab <arabm@google.com>
Reviewed-by: Martin Šrámek <msramek@chromium.org>
Reviewed-by: Mohamad Arab <arabm@google.com>
Auto-Submit: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312836}