If the branch associated with the condition is kDead, the current
node will be killed anyway, so let us just survive the lowering.

Bug: chromium:935092
Change-Id: If7b39e3b5452d6c9bc5199080eb38725e6c4eab5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1488769Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60143}