With this CL it is not possible anymore to initialize a func ref table
with extern ref ref.null.

R=manoskouk@chromium.org

Change-Id: If6023da6fc21844dd813cc6191f2a4ca595f8b00
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2912577
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74727}