First discovery by the names section fuzzer I think. During the decoding
of the names of locals only ok() of the outer decoder was checked, not
the ok() of the actual names section decoder.

R=tizer@chromium.org
BUG=chromium:684855

Review-Url: https://codereview.chromium.org/2648383007
Cr-Commit-Position: refs/heads/master@{#42880}