Fix crash when displaying a null certificate.

Fix crash when displaying a null certificate.

This regressed in r417444. Previously (https://codereview.chromium.org/2327433002/diff/250001/chrome/browser/certificate_viewer.cc) we would check that the certificate id sent by the renderer was valid (say because renderer died). Races could also happen now, in that the page might navigate right after user presses certificate viewer button and the last committed entry wouldn't have a certificate.

BUG=646882
Committed: https://crrev.com/86e4f0c45cb22e575d7c5a373ebe40c66ec1f2eb
Cr-Commit-Position: refs/heads/master@{#418644}

[jam, 2016-09-14 17:45:17]

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

[commit-bot: I haz the power, 2016-09-14 17:45:48]

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

[jam, 2016-09-14 17:45:48]

jam@chromium.org changed reviewers:
+ pfeldman@chromium.org

[commit-bot: I haz the power, 2016-09-14 19:16:13]

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

[commit-bot: I haz the power, 2016-09-14 19:16:14]

Dry run: This issue passed the CQ dry run.

[pfeldman, 2016-09-14 19:30:39]

lgtm

[jam, 2016-09-14 19:35:36]

The CQ bit was checked by jam@chromium.org

[commit-bot: I haz the power, 2016-09-14 19:36:22]

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, 2016-09-14 19:43:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-09-14 19:44:41]

Description was changed from

==========
Fix crash when displaying a null certificate.

This regressed in r417444. Previously
(https://codereview.chromium.org/2327433002/diff/250001/chrome/browser/certifi...)
we would check that the certificate id sent by the renderer was valid (say
because renderer died). Races could also happen now, in that the page might
navigate right after user presses certificate viewer button and the last
committed entry wouldn't have a certificate.

BUG=646882
==========

to

==========
Fix crash when displaying a null certificate.

This regressed in r417444. Previously
(https://codereview.chromium.org/2327433002/diff/250001/chrome/browser/certifi...)
we would check that the certificate id sent by the renderer was valid (say
because renderer died). Races could also happen now, in that the page might
navigate right after user presses certificate viewer button and the last
committed entry wouldn't have a certificate.

BUG=646882

Committed: https://crrev.com/86e4f0c45cb22e575d7c5a373ebe40c66ec1f2eb
Cr-Commit-Position: refs/heads/master@{#418644}
==========

[commit-bot: I haz the power, 2016-09-14 19:44:42]

Patchset 1 (id:??) landed as
https://crrev.com/86e4f0c45cb22e575d7c5a373ebe40c66ec1f2eb
Cr-Commit-Position: refs/heads/master@{#418644}