Preserve isearch match data when expanding fragments

[Gleek]

Running isearch sometimes I get this backtrace:

Debugger entered--Lisp error: (args-out-of-range 0 0)
  agent-shell-ui--isearch-filter-predicate(0 1)
  isearch-lazy-highlight-buffer-update()
  apply(isearch-lazy-highlight-buffer-update nil)
  timer-event-handler([t 27305 6365 618880 nil isearch-lazy-highlight-buffer-update nil nil 0 nil])
  sit-for(0)
  isearch-lazy-highlight-new-loop()
  isearch-post-command-hook()

isearch-filter-predicate must preserve match data. Expanding a fragment calls helpers that can run another search (probably some regex matching code in markdown renderer) which overrides the original match-data. Wrapping the whole thing in save-match-data restores the original match data so isearch is happy.

Single line change, best viewed without whitespace: https://github.com/xenodium/agent-shell/pull/827/changes?w=1

Checklist

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[xenodium]

Thanks for the improvement. Mind rebasing on to main?

[Gleek]

Thanks for the improvement. Mind rebasing on to main?

done

[xenodium]

Thank you!