Type check the implicit else-branch of multi-value one-armed if blocks.

R=ahaas@chromium.org
BUG=chromium:1019648

Change-Id: I939d712e9cffd531c764f105cfb2e7c148d3b7dc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1890095
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64681}