This CL fixes the zero-count and overlapping cases for the table.copy
bytecode.

R=mstarzinger@chromium.org
CC=binji@chromium.org
BUG=v8:7747

Change-Id: I6211e4c899621069ebf8bc088b3ab4e80c7bbd0a
Reviewed-on: https://chromium-review.googlesource.com/c/1417172
Commit-Queue: Ben Titzer <titzer@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58887}