Fix TryGet returning false for empty subranges with exclusive parent boundaries

[Copilot]

TryGet(Range subRange, ...) incorrectly returned false for empty-but-contained subranges when the parent range had exclusive boundaries. Example: parent (10,20] with subrange (10,10] returned false instead of an empty RangeData.

Root Cause

After adjusting indices for boundary inclusiveness, endIndex could become negative for empty ranges. The negative-index guard rejected these before the empty-range check (count <= 0) could execute.

Changes

• Reordered validation logic: Check count <= 0 before validating index bounds
• Added comment: Clarified why empty-range detection must precede overflow checks
• Test coverage: Added cases for empty subranges at exclusive boundaries

// Before: negative endIndex causes early return false
var count = endIndex - startIndex + 1;
if (startIndex < 0 || endIndex < 0) return false;  // ❌ Blocks empty ranges
if (count <= 0) return Empty(...);

// After: empty ranges detected first
var count = endIndex - startIndex + 1;
if (count <= 0) return Empty(...);  // ✅ Handles empty correctly
if (startIndex < 0 || endIndex < 0) return false;

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[Copilot]

Pull request overview

This PR fixes a bug where TryGet(Range subRange, ...) incorrectly returned false for empty subranges when the parent range had exclusive boundaries. The issue occurred because negative indices (from boundary adjustments) were rejected before empty-range logic could execute.

Changes:

• Reordered validation logic to check for empty ranges (count <= 0) before validating index bounds
• Added clarifying comment explaining the ordering requirement
• Added three test cases covering empty subranges at exclusive boundaries

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Intervals.NET.Data/RangeData.cs	Moved empty-range check before negative-index guard to properly handle empty subranges at exclusive boundaries
tests/Intervals.NET.Data.Tests/RangeDataTests.cs	Added three test cases verifying empty subranges return true with empty data when at exclusive parent boundaries

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