fix: ChunkString returns empty slice for empty input (fixes #788)

[nghiack7]

Summary

ChunkString("", n) was returning [""] (a one-element slice containing an empty string) instead of [] (an empty slice). This was inconsistent with Chunk([]rune{}, n) which correctly returns an empty slice.

Root Cause

The early-return guard if size >= len(str) { return []T{str} } always fires when str is empty because any positive size satisfies size >= 0. So it returned []T{""} instead of an empty slice.

Fix

Add an explicit early-return for the empty-string case before the size check:

if len(str) == 0 {
    return []T{}
}

Test

Updated the existing test case (which already carried a // @TODO: should be [] comment referencing #788) to assert the correct behavior.

// Before
ChunkString("", 2) // => [""]

// After  
ChunkString("", 2) // => []

Full test suite passes with no regressions.

Fixes #788

[nghiack7]

Friendly ping — this is a one-line fix for ChunkString("", n) returning [""] instead of []. All tests pass ✅. Fixes #788.

[samber]

Hello @nghiack7

Sure, this is a one-line fix, but it would break lots of code. The #788 is not fixed because the change impact is huge.

Adding a label #breaking-change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.58%. Comparing base (6f2b2bc) to head (fe94cf7).
⚠️ Report is 14 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #880   +/-   ##
=======================================
  Coverage   92.57%   92.58%           
=======================================
  Files          32       32           
  Lines        5067     5069    +2     
=======================================
+ Hits         4691     4693    +2     
  Misses        273      273           
  Partials      103      103           

Flag	Coverage Δ
unittests	92.58% <100.00%> (+<0.01%)	⬆️

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