cut: fix -s flag ignored when delimiter is newline

[rynewang]

When using newline as the delimiter (-d $'\n') with -s (only-delimited), cut should suppress lines that do not contain the delimiter. However, cut_fields_newline_char_delim() was not checking the only_delimited flag, causing it to always output even when -s was specified.

The Bug

# Expected (GNU):
printf 'abc' | cut -d $'\n' -f1 -s    # (no output)

# Actual (before fix):
printf 'abc' | cut -d $'\n' -f1 -s    # abc\n

Changes

• Adds only_delimited parameter to cut_fields_newline_char_delim()
• Checks if input has no delimiter and only_delimited is true, returns early without output
• Adds test case for newline delimiter with -s flag

Fixes #10012

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cut/cut. tests/cut/cut is passing on 'main'. Maybe you have to rebase?

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[codspeed-hq]

Merging this PR will not alter performance

✅ 284 untouched benchmarks
⏩ 38 skipped benchmarks¹

---

_{Comparing rynewang:fix-cut-newline-delimiter-only-delimited (e613550) with main (ec7e81e)}

Footnotes

1. 38 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/pr/bounded-memory. tests/pr/bounded-memory is passing on 'main'. Maybe you have to rebase?

[cakebaker]

Closing as it has been superseded by #11143.

Anyway, thanks for the PR!