empty /manifest.js.gz response as of 520be116

[Kyle Meyer <kyle@kyleam.com>]

I recently upgraded a server from 08b649735 to 5860b498a and noticed
that grok-pull didn't bring in any updates.  It looks like what's going
on is that the top-level /manifest.js.gz endpoint is now coming up
empty.

A minimal example on 5860b498a:

  $ git clone --mirror https://try.public-inbox.org/test test
  $ export PI_CONFIG="$PWD/config"
  $ public-inbox-init -V1 test test/ \
     http://localhost:8080/test test@public-inbox.org
  $ public-inbox-index -v test
  $ public-inbox-httpd &

  $ curl -fsS http://localhost:8080/manifest.js.gz | zcat | jq
  {}

On 08b649735, the output is

  {
    "/test": {
      "reference": null,
      ...
    }
  }

Bisecting with the script below points to 520be116 (www_listing: start
updating for pagination + search, 2021-06-23).

--8<---------------cut here---------------start------------->8---
#!/bin/sh

perl Makefile.PL && make && sudo make install || exit 125

# Local clone of https://try.public-inbox.org/test
pi_test=/tmp/pi-test

cd "$(mktemp -d "${TMPDIR:-/tmp}"/pi-XXXXXXX)"

export PI_CONFIG="$PWD/config"

git clone --mirror "$pi_test" test
public-inbox-init -V1 test test/ \
                  http://localhost:8080/test test@public-inbox.org
public-inbox-index -v test

trap 'trap - TERM && pkill -P $$' INT TERM EXIT
public-inbox-httpd &

sleep 1

curl -fsS http://localhost:8080/manifest.js.gz | zcat | jq -e '.["/test"]'
--8<---------------cut here---------------end--------------->8---