Do not set is_url_removed_by_policy on empty referrer chain entry

Bug: 1445762
Change-Id: I73e06db469167c159ebaef40b198487532595c1a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4559886


Commit-Queue: Xinghui Lu <xinghuilu@chromium.org>
Reviewed-by: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1148623}