fix(format-po-gettext): bad return during mapping with serializePlurals

[stovmascript]

Description

In v4 this formatter can return undefined when passing a non-plural message to the serializePlurals function, which will throw later when serializing the PO file. The original item should be returned instead.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Fixes # (issue)

Checklist

• I have read the CONTRIBUTING and CODE_OF_CONDUCT docs
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
js-lingui	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 21, 2023 4:46pm

[github-actions]

size-limit report 📦

Path	Size
./packages/core/dist/index.mjs	2.76 KB (0%)
./packages/detect-locale/dist/index.mjs	721 B (0%)
./packages/react/dist/index.mjs	1.59 KB (0%)
./packages/remote-loader/dist/index.mjs	7.24 KB (0%)

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.19 🎉

Comparison is base (ff96df4) 75.82% compared to head (39a8b26) 76.01%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1707      +/-   ##
==========================================
+ Coverage   75.82%   76.01%   +0.19%     
==========================================
  Files          79       79              
  Lines        2039     2039              
  Branches      524      524              
==========================================
+ Hits         1546     1550       +4     
+ Misses        378      376       -2     
+ Partials      115      113       -2     

Impacted Files	Coverage Δ
packages/format-po-gettext/src/po-gettext.ts	83.33% <100.00%> (+4.16%)	⬆️

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[timofei-iatsenko]

Thanks for tackling this. Please create a test case covering this.

[stovmascript]

@thekip Done.

[timofei-iatsenko]

@stovmascript big thanks!