Fix an error 'Use-of-uninitialized-value in CPDF_Function::Call'

Fix an error 'Use-of-uninitialized-value in CPDF_Function::Call'

This issue was introduced in https://codereview.chromium.org/886953002/.

BUG=454280
R=tsepez@chromium.org

Committed: https://pdfium.googlesource.com/pdfium/+/493f5c622d23b8011cb8cdbacbb7258afe7d4ba1

[jun_fang, 2015-02-12 01:11:49]

jun_fang@foxitsoftware.com changed reviewers:
+ thestig@chromium.org, tsepez@chromium.org

[jun_fang, 2015-02-12 01:11:50]

Hi Tom and Lei,

Please review this change. Thanks!

[Tom Sepez, 2015-02-12 18:06:47]

https://codereview.chromium.org/869343008/diff/1/core/src/fpdfapi/fpdf_page/f...
File core/src/fpdfapi/fpdf_page/fpdf_page_func.cpp (right):

https://codereview.chromium.org/869343008/diff/1/core/src/fpdfapi/fpdf_page/f...
core/src/fpdfapi/fpdf_page/fpdf_page_func.cpp:570: FX_SAFE_INT32 bitpos1 =
m_nOutputs - 1 > 0 ? m_nOutputs - 1 : 0;
Looking at the original code, I don't remember why we subtracted 1 here.  Is
that a mistake?

[jun_fang, 2015-02-12 18:13:35]

https://codereview.chromium.org/869343008/diff/1/core/src/fpdfapi/fpdf_page/f...
File core/src/fpdfapi/fpdf_page/fpdf_page_func.cpp (right):

https://codereview.chromium.org/869343008/diff/1/core/src/fpdfapi/fpdf_page/f...
core/src/fpdfapi/fpdf_page/fpdf_page_func.cpp:570: FX_SAFE_INT32 bitpos1 =
m_nOutputs - 1 > 0 ? m_nOutputs - 1 : 0;
On 2015/02/12 18:06:46, Tom Sepez wrote:
> Looking at the original code, I don't remember why we subtracted 1 here.  Is
> that a mistake?

This judge is used to ensure 'bitpos.ValueOrDie() + j * m_nBitsPerSample' at
line 577 not to overflow. The maxium of 'j' is  m_nOutputs - 1 .

[Tom Sepez, 2015-02-12 20:37:26]

that a mistake?
> 
> This judge is used to ensure 'bitpos.ValueOrDie() + j * m_nBitsPerSample' at
> line 577 not to overflow. The maxium of 'j' is  m_nOutputs - 1 .
Alright, LGTM.

[jun_fang, 2015-02-12 20:40:42]

Committed patchset #1 (id:1) manually as
493f5c622d23b8011cb8cdbacbb7258afe7d4ba1 (presubmit successful).