Follow on from #4375 with issue #4374

Problem:
Some Sys plugin results (e.g 'Settings') do not show up in 'Empty Last Query' query style mode after they are selected, and would only show when re-queried or clearing of a new query.

Cause:
When plugin actions call Context.API.HideMainWindow() directly it does a re-query before the result is added to last history items and consequently the second Hide() call at the end of OpenResultAsync(string) would not trigger a re-query because QueryText is already "", so QueryText != queryText is false. Without a re-query the newly added last history item does not get added to result list display.

Fix:
Move _history.Add(result) to immediately after the result == null check, before ExecuteAsync(ActionContext) is called, guaranteeing that history is updated before any possible Hide() invocation — whether triggered from inside the plugin action or from the explicit Hide() call afterward.

Tested:

• Results like 'Settings' from Sys plugin show up after selection

Summary by cubic

Fixes a race that caused the last selected system plugin result (e.g., “Settings”) to not appear in “Empty Last Query” mode. We now record the history entry before executing the action, so plugin-triggered re-queries don’t drop it.

• Summary of changes
  • Changed: In OpenResultAsync, add the selected result to history before ExecuteAsync and any Hide() call; applies only to query results (not context menu/history).
  • Added: Set lastHistoryIndex = 1 at the time of the early history write to ensure correct positioning in history.
  • Removed: The late _history.Add block after ExecuteAsync, avoiding missed updates and duplicate logic.
  • Memory usage: No impact; same history size and allocations, only call order changed.
  • Security: No new risks; internal ordering change only, no new I/O or permissions.
  • Tests: No new unit tests; manually verified that Sys plugin entries like “Settings” now appear immediately in “Empty Last Query” mode.

^{Written for commit a250e79. Summary will update on new commits.}