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

CHANGELOG.md

@@ -6,6 +6,8 @@ CHANGELOG
 - Fixed an escape sequence split across reads being parsed as a fragment, which leaked the rest into the query (#4899)
     - e.g. A terminal answering the startup `DECRQM` query late left `?2004;2$y`, CTRL-UP left `5A`, and SGR mouse input left `0;1;1M`
 - Fixed `--tiebreak=pathname` not detecting the last path separator when the line contains a non-ASCII character before it (#4902)
+- Fixed `progress` in the `--listen` status payload staying at 100 while a new search was running, which made a snapshot with a new query and the previous result set look complete (#4903)
+    - It is now reset when a search starts and reaches 100 on the final result, so `progress` of 100 means the matches belong to the query reported next to them
 - Fixed adaptive height not reserving a line for the divider of an inline header or footer border, so the list came up one line short for each of them (#4904)
     - e.g. `seq 10 | fzf --height=~100% --list-border --header-lines=1 --header-lines-border=inline`
 - Vim plugin