Return empty optional instead of optional with empty Map on failure.

Bug: v8:7790, chromium:1323119
Change-Id: I1e6e9e2361d12d0f8d106a7929221d3116d0d547
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3650715
Auto-Submit: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80564}