When preparsing and detecting a sloppy block function redefinition then
don't mark the variable as assigned to make it consistent with the eager
parser.

Bug: chromium:1053364
Change-Id: Iec7c24db80014bfe73ee41a4f3bb7a41a354cef2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2241511
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68415}