Fix cluster-fuzz found regression in d8 Workers

Fix cluster-fuzz found regression in d8 Workers

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

Committed: https://crrev.com/abaa094a2b1d9e2d49bf1a704d5ebd4675160ff8
Cr-Commit-Position: refs/heads/master@{#29388}

[Michael Starzinger, 2015-06-30 16:46:08]

LGTM.

[binji, 2015-06-30 16:47:05]

The CQ bit was checked by binji@chromium.org

[commit-bot: I haz the power, 2015-06-30 16:47:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1216853003/1

[commit-bot: I haz the power, 2015-06-30 16:49:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-30 16:49:17]

Patchset 1 (id:??) landed as
https://crrev.com/abaa094a2b1d9e2d49bf1a704d5ebd4675160ff8
Cr-Commit-Position: refs/heads/master@{#29388}