fix panic in analyze-string

[frankarensmeier]

Fix panic in analyze-string with non-participating optional groups

When optional groups (e.g. ([0-9]{1,2})?) don't participate in a match, they produce zero-length group entries. For these entries, when no parent group end-event exists at the same position, the start and end events were inserted in the wrong order (end before start). This caused on_group_end() to pop from an empty stack, panicking with unwrap() on None.

Fix: swap the event insertion order in the or_insert_with branch from (-i, i) to (i, -i), matching the and_modify branch which already inserts start before end.

Add regression test with regex ([0-9]{1,2})?\s?(...)?...\s?([0-9]{4}) matching "1949" where groups 1 and 2 are optional and don't participate.

[Copilot]

Pull request overview

Fixes a panic in Regex::analyze when optional capturing groups don’t participate and end up represented as zero-length captures, by ensuring zero-length group “start/end” events are always inserted in a safe order.

Changes:

• Adjust event insertion order for zero-length capture groups to insert “start” before “end”, preventing on_group_end() from popping an empty stack.
• Add a regression test covering optional groups that don’t participate for a realistic date-like pattern.

Reviewed changes

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

File	Description
regexml/src/analyze_string.rs	Fixes action ordering for zero-length group events in the or_insert_with path to avoid panics.
regexml/tests/test_qt_analyze_string.rs	Adds a regression test exercising optional non-participating groups to ensure analyze() no longer panics.

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