privacy-hub: Fix crash on NotifyGeolocationPermissionChanged() in Perso app

Personalization app would crash on system geolocation access level
changes. I could only reproduce this for users from a domain other than
Google. Apparently the Ambient mode is not yet allowed for the
enterprise domains. Thus the `PersonalizationAppAmbientProviderImpl`
would not bind the `ambient_observer_remote_` endpoint, which was
asserted in the `NotifyGeolocationPermissionChanged()`.

Modify this assertion with returning preemptively if the
`ambient_observer_remote_` endpoint is not bound.

Bug: b:344653836
Change-Id: I808581d60059b9e4303a36a32e194846dbf1b940
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5610699


Commit-Queue: Zauri Meshveliani <zauri@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312734}