When --async-stack-traces is on and there's an exception from within an
async_hook "after" handler, we will be faced with a settled promise. In
that case we cannot do anything, since the promise will not have any
reactions on it anymore, but we should also not crash of course.

Bug: chromium:896700, v8:7522
Change-Id: I6e3d212d0433da40740489ff7421c5a98cf9bff3
Reviewed-on: https://chromium-review.googlesource.com/c/1290550Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56801}