Create small default segment if out of heap

[DedeHai]

Fallback path was missing. If out of heap and no segments are created the UI shows "no segments" error and disables most control elements which is confusing.

Summary by CodeRabbit

• Bug Fixes
  • Improved segment initialization when automatic segment creation fails.
  • Added a fallback to ensure a default segment is available when no active segments can be created.
  • Improved handling for matrix and one-dimensional LED configurations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: bb0d56a4-e8cf-4835-906a-8690455abf3e

📥 Commits

Reviewing files that changed from the base of the PR and between e391183 and 033957d.

📒 Files selected for processing (1)

• wled00/FX_fcn.cpp

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Walkthrough

Changes

Segment recovery

Layer / File(s)	Summary
Active segment fallback handling wled00/FX_fcn.cpp	resetSegments() now checks active segments before creating its default fallback, and makeAutoSegments() resets segments when automatic creation leaves none active.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• wled/WLED#4811: Both changes modify WS2812FX::makeAutoSegments() in wled00/FX_fcn.cpp.

Suggested reviewers: npabisz, willmmiles

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main change: creating a small default segment when heap allocation prevents segment creation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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