If parsing fails in ScopeIterator::TryParseAndRetrieveScopes, the
intention was to fail silently (see the TODO there). However,
closure_scope_ being nullptr caused us to fail less silently.

This alone is not enough for fixing chromium:1316811 but the other
fixes needed are sufficiently unrelated.

Bug: chromium:1316811
Change-Id: I4eb0f5a13fa4da5fd5dd7ff76a1aa1a6a8ee4c63
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3716477Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81300}