Fix undefined behavior in libpng

Fix undefined behavior in libpng

Check for a null source before calling memcpy.

BUG=skia:5390
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2040433002

Committed: https://skia.googlesource.com/skia/+/1915b0bab2b48cf8bf85dc49e76994b033f25450

[scroggo_chromium, 2016-06-03 15:31:30]

Description was changed from

==========
Fix undefined behavior in libpng

Check for a null source before calling memcpy.

BUG=skia:5390
==========

to

==========
Fix undefined behavior in libpng

Check for a null source before calling memcpy.

BUG=skia:5390
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2040433002
==========

[scroggo, 2016-06-03 15:36:03]

scroggo@google.com changed reviewers:
+ msarett@google.com, scroggo@google.com

[scroggo, 2016-06-03 15:36:03]

I figured the most expedient thing to do would be to fix the bug in our copy,
and then work to get it upstreamed. I am running on the ASAN trybot in case
there are other problems.

[msarett, 2016-06-03 15:38:16]

Sounds good to me.

lgtm

[scroggo, 2016-06-03 16:14:08]

The CQ bit was checked by scroggo@google.com

[commit-bot: I haz the power, 2016-06-03 16:14:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2040433002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/2040433002/1

[commit-bot: I haz the power, 2016-06-03 16:36:56]

Description was changed from

==========
Fix undefined behavior in libpng

Check for a null source before calling memcpy.

BUG=skia:5390
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2040433002
==========

to

==========
Fix undefined behavior in libpng

Check for a null source before calling memcpy.

BUG=skia:5390
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2040433002

Committed:
https://skia.googlesource.com/skia/+/1915b0bab2b48cf8bf85dc49e76994b033f25450
==========

[commit-bot: I haz the power, 2016-06-03 16:36:57]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/1915b0bab2b48cf8bf85dc49e76994b033f25450