When using promise hooks we can actually end up in capturing stack trace
with an async generator on the stack whose queue is empty, and we need
to gracefully handle that case as well.

Fixed: chromium:1015945
Change-Id: Ia459e7444b373ecab01ca6900a781fd8b4021d1a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1870230
Auto-Submit: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64403}