Fix stale progress in --listen status payload (#4907)

- progress was set to 100 by every UpdateList, partial results included,
  and never reset when a search started
- So a GET could report a new query, the previous result set, and
  progress 100, and a client had no way to tell it was stale
- Now cleared where the search is requested and set to 100 only on the
  final result. Query and the reset happen in the same locked section
  that dumpStatus locks, so query == X with progress 100 means the
  matches belong to X

Fix #4903

src/terminal.go

@@ -2059,7 +2059,9 @@ func (t *Terminal) UpdateList(result MatchResult) {
 		prevIndex = t.targetIndex
 		t.targetIndex = minItem.Index()
 	}
-	t.progress = 100
+	if result.final() {
+		t.progress = 100
+	}
 	t.merger = merger
 	t.resultMerger = merger
 	t.passMerger = result.passMerger
@@ -8597,6 +8599,7 @@ func (t *Terminal) Loop() error {
 		reload := changed || newCommand != nil
 		if reload {
 			t.wait.searching = true
+			t.progress = 0
 		}
 		var reloadRequest *searchRequest
 		if reload {