[wasm] Fix decoder for null data

[wasm] Fix decoder for null data

If passing <nullptr, 0> to the decoder and trying to decode something,
it correctly detects the error and sets an error message, but still
returns true on ok(), and returns a valid result.
I triggered this error by passing a null Vector, returned by FindSection(), to
the decoder.

R=titzer@chromium.org

Committed: https://crrev.com/e7a00891495d123f68b7fe0f2a43839e34591c8e
Cr-Commit-Position: refs/heads/master@{#40204}

[Clemens Hammacher, 2016-10-11 15:39:46]

The CQ bit was checked by clemensh@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-10-11 15:39:54]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-11 16:05:59]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-10-11 16:05:59]

Dry run: This issue passed the CQ dry run.

[titzer, 2016-10-12 09:09:06]

lgtm

[Clemens Hammacher, 2016-10-12 09:09:23]

The CQ bit was checked by clemensh@chromium.org

[commit-bot: I haz the power, 2016-10-12 09:09:26]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-12 09:11:47]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-12 09:12:01]

Description was changed from

==========
[wasm] Fix decoder for null data

If passing <nullptr, 0> to the decoder and trying to decode something,
it correctly detects the error and sets an error message, but still
returns true on ok(), and returns a valid result.
I triggered this error by passing a null Vector, returned by FindSection(), to
the decoder.

R=titzer@chromium.org
==========

to

==========
[wasm] Fix decoder for null data

If passing <nullptr, 0> to the decoder and trying to decode something,
it correctly detects the error and sets an error message, but still
returns true on ok(), and returns a valid result.
I triggered this error by passing a null Vector, returned by FindSection(), to
the decoder.

R=titzer@chromium.org

Committed: https://crrev.com/e7a00891495d123f68b7fe0f2a43839e34591c8e
Cr-Commit-Position: refs/heads/master@{#40204}
==========

[commit-bot: I haz the power, 2016-10-12 09:12:02]

Patchset 1 (id:??) landed as
https://crrev.com/e7a00891495d123f68b7fe0f2a43839e34591c8e
Cr-Commit-Position: refs/heads/master@{#40204}