[heap] Fix NewEmptyCode initialisation

NewEmptyCode was missing the initialisation of three fields.
These were crashing when running with --verify-heap.

Bug: v8:11872
Change-Id: I679f0d2d68c5594b0e9700b26c031483c3d46b68
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2999095


Auto-Submit: Victor Gomes <victorgomes@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75511}