Fix SkIStream nits.

Fix SkIStream nits.

Fix comment, constness of one field, and delete already checks for NULL.

TBR=reed@google.com
Trivial change to debatably public api.

Committed: https://skia.googlesource.com/skia/+/44af7ba4bc571110f02f31dd71a8fd4dc7e6bfd2

[bungeman-skia, 2015-01-22 14:28:25]

bungeman@google.com changed reviewers:
+ scroggo@google.com

[bungeman-skia, 2015-01-22 14:28:31]

The CQ bit was checked by bungeman@google.com

[scroggo, 2015-01-22 14:29:18]

lgtm

[commit-bot: I haz the power, 2015-01-22 14:29:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/868643003/1

[commit-bot: I haz the power, 2015-01-22 14:29:30]

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

[commit-bot: I haz the power, 2015-01-22 14:29:31]

Presubmit check for 868643003-1 failed and returned exit status 1.

Running presubmit commit checks ...

** Presubmit ERRORS **
Since the CL is editing public API, you must have an LGTM from one of:
('reed@chromium.org', 'reed@google.com', 'bsalomon@chromium.org',
'bsalomon@google.com', 'djsollen@chromium.org', 'djsollen@google.com')

Was the presubmit check useful? If not, run "git cl presubmit -v"
to figure out which PRESUBMIT.py was run, then run git blame
on the file to figure out who to ask for help.

[bungeman-skia, 2015-01-22 15:26:03]

The CQ bit was checked by bungeman@google.com

[commit-bot: I haz the power, 2015-01-22 15:26:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/868643003/1

[commit-bot: I haz the power, 2015-01-22 15:33:54]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/44af7ba4bc571110f02f31dd71a8fd4dc7e6bfd2