v8::Internal::List will DCHECK when indexing out of the array, even if just to
get the address, and the value is never used. So this construct will fail:

    memcpy(p, &data[0], length);

When data is empty and length is 0.

BUG=chromium:505778
R=mstarzinger@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/1216853003

Cr-Commit-Position: refs/heads/master@{#29388}