When a GC happens during context deserialization,
NativeContext::retained_maps might be uninitialized and not store a
WeakArrayList but Smi 0.

Bug: v8:12198
Change-Id: I03c1dfaa013c47907af67bb13b9277d67ca5ffae
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3259662Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77692}