Automatic Fullscreen: Fix null HostContentSettingsMap deref

Some WebContents have null settings maps, e.g. profile switcher.

Bug: 40941384
Change-Id: Ia53dc0a6f9db99826c3a3a3bf66c9aac590290a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5425577


Commit-Queue: Brad Triebwasser <btriebw@chromium.org>
Auto-Submit: Mike Wasserman <msw@chromium.org>
Reviewed-by: Brad Triebwasser <btriebw@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283412}