Previously SnapshotCreator demanded a blob to be created before
it can be destructed in debug build, this patch removes the
DCHECK so that the embedder can choose not to create the blob
when e.g. the snapshot building isn't successful due to errors.

Change-Id: I72939be1e0d79b257b9761f48a72e45325a1f6d8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3716682Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Cr-Commit-Position: refs/heads/main@{#81644}