If the Maybe is nothing or the MaybeLocal is empty, it means that the
API call either threw an exception or an exception was already pending.

In that case, the embedder needs to handle the exception or otherwise
react to the failed API call.

BUG=v8:3929
R=svenpanne@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/1022803002

Cr-Commit-Position: refs/heads/master@{#27298}