If context filtration fails, ensure that we still include an empty
sample. This ensures that we can properly terminate stacks.

Bug: chromium:956688
Change-Id: I3edeb3434960c420e24827c209055f7c378361bf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3058053Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Cr-Commit-Position: refs/heads/master@{#75980}