RequestSweep started an array buffer sweeping task even when there was
no work.

Bug: chromium:1045937
Change-Id: Ieb0835284f898dbc9b899d2b4118d9f7f6108a6f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2020961
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66004}