Respect ToUnicode map when it maps a charcode to unicode 0

Use ToUnicode mapping even when unicode is 0.

CPDF_Font::UnicodeFromCharcode returns 0 only if ToUnicode map maps the
charcode to 0. CPDF_SimpleFont::UnicodeFromCharcode and CPDF_CID_Font::
UnicodeFromCharCode return 0 only if the call to CPDF_Font returns 0.
In other cases, these methods return an empty string. So when
processing text, a 0 return from the method should not be replaced
with the charcode.

BUG=pdfium:583
Committed: https://pdfium.googlesource.com/pdfium/+/84be3a3cfec5107aac9a58ea00b58b733d393c7d

[npm, 2016-09-15 16:02:42]

Description was changed from

==========
Respect ToUnicode map when it maps a charcode to unicode 0

CPDF_Font::UnicodeFromCharcode returns 0 only if ToUnicode map maps the
charcode to 0. CPDF_SimpleFont::UnicodeFromCharcode and CPDF_CID_Font::
UnicodeFromCharCode return 0 only if the call to CPDF_Font returns 0.
In other cases, these methods return an empty string. So when
processing text, a 0 return from the method should not be replaced
with the charcode.

BUG=pdfium:583
==========

to

==========
Use ToUnicode mapping even when unicode is 0.

CPDF_Font::UnicodeFromCharcode returns 0 only if ToUnicode map maps the
charcode to 0. CPDF_SimpleFont::UnicodeFromCharcode and CPDF_CID_Font::
UnicodeFromCharCode return 0 only if the call to CPDF_Font returns 0.
In other cases, these methods return an empty string. So when
processing text, a 0 return from the method should not be replaced
with the charcode.

BUG=pdfium:583
==========

[npm, 2016-09-15 16:02:42]

npm@chromium.org changed reviewers:
+ dsinclair@chromium.org, halcanary@chromium.org, weili@chromium.org

[npm, 2016-09-15 16:03:26]

PTAL

[npm, 2016-09-15 16:03:43]

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

[commit-bot: I haz the power, 2016-09-15 16:03:49]

Dry run: 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, 2016-09-15 16:16:39]

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

[commit-bot: I haz the power, 2016-09-15 16:16:40]

Dry run: This issue passed the CQ dry run.

[dsinclair, 2016-09-15 17:43:39]

Code lg to me. Can we create a unit test or some kind of test to verify this
doesn't regress?

[npm, 2016-09-15 20:06:41]

PTAL

[npm, 2016-09-15 20:06:45]

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

[commit-bot: I haz the power, 2016-09-15 20:06:56]

Dry run: 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, 2016-09-15 20:22:07]

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

[commit-bot: I haz the power, 2016-09-15 20:22:08]

Dry run: This issue passed the CQ dry run.

[dsinclair, 2016-09-15 20:25:13]

lgtm

[npm, 2016-09-15 20:27:01]

The CQ bit was checked by npm@chromium.org

[commit-bot: I haz the power, 2016-09-15 20:27:06]

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, 2016-09-15 20:27:23]

Description was changed from

==========
Use ToUnicode mapping even when unicode is 0.

CPDF_Font::UnicodeFromCharcode returns 0 only if ToUnicode map maps the
charcode to 0. CPDF_SimpleFont::UnicodeFromCharcode and CPDF_CID_Font::
UnicodeFromCharCode return 0 only if the call to CPDF_Font returns 0.
In other cases, these methods return an empty string. So when
processing text, a 0 return from the method should not be replaced
with the charcode.

BUG=pdfium:583
==========

to

==========
Use ToUnicode mapping even when unicode is 0.

CPDF_Font::UnicodeFromCharcode returns 0 only if ToUnicode map maps the
charcode to 0. CPDF_SimpleFont::UnicodeFromCharcode and CPDF_CID_Font::
UnicodeFromCharCode return 0 only if the call to CPDF_Font returns 0.
In other cases, these methods return an empty string. So when
processing text, a 0 return from the method should not be replaced
with the charcode.

BUG=pdfium:583

Committed:
https://pdfium.googlesource.com/pdfium/+/84be3a3cfec5107aac9a58ea00b58b733d39...
==========

[commit-bot: I haz the power, 2016-09-15 20:27:24]

Committed patchset #2 (id:20001) as
https://pdfium.googlesource.com/pdfium/+/84be3a3cfec5107aac9a58ea00b58b733d39...