Fix bmp bug in ReadHeader()

Fix bmp bug in ReadHeader()

For BmpMaskCodecs, we need to skip any offset after the
header to get to the start of pixel data.

Before this fix, we only skipped this data when codecOut
is non-NULL (instead of on every call to ReadHeader()).

https://gold.skia.org/search?q=1&neg=true&unt=false&query=name%3Drgb16-565pal.bmp_0.200%26name%3Drgb16-565pal.bmp%26name%3Drgb16-565pal.bmp_0.250%26name%3Drgb16-565pal.bmp_0.333%26name%3Drgb16-565pal.bmp_0.375%26name%3Drgb16-565pal.bmp_0.400%26name%3Drgb16-565pal.bmp_0.500%26source_type%3Dimage
BUG=skia:

Committed: https://skia.googlesource.com/skia/+/9aa32d1d830c030000c1178b1297035a9b53d5bc

[msarett, 2015-09-01 20:53:36]

Patchset #1 (id:1) has been deleted

[msarett, 2015-09-01 20:57:08]

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

[scroggo, 2015-09-01 21:31:26]

lgtm

https://codereview.chromium.org/1318393004/diff/20001/src/codec/SkBmpCodec.cpp
File src/codec/SkBmpCodec.cpp (right):

https://codereview.chromium.org/1318393004/diff/20001/src/codec/SkBmpCodec.cp...
src/codec/SkBmpCodec.cpp:462: //                 Maybe we don't want to try to
decode corrupt images?
All good questions. I think we should support an implicit zero offset if this is
a common use case.

If the rest of our code is robust, getting some false positives here (i.e. we
assumed the offset was zero and the rest of the file was not valid) is probably
okay.

[scroggo, 2015-09-01 21:31:27]

lgtm

lgtm

[msarett, 2015-09-01 21:35:22]

The CQ bit was checked by msarett@google.com

[commit-bot: I haz the power, 2015-09-01 21:35:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1318393004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1318393004/20001

[commit-bot: I haz the power, 2015-09-01 21:40:49]

Committed patchset #1 (id:20001) as
https://skia.googlesource.com/skia/+/9aa32d1d830c030000c1178b1297035a9b53d5bc