Problem: when the indexer hasn't finished some pages show an error

Some slow queries we only do once an hour by a component known as the "indexer", it puts a bunch of lookup maps in an atom.

When the app starts it takes a few minutes before this index map is populated, at that point we should show empty pages or some kind of "sit tight" page, but not a 500 error (NullPointerException) as we do now.

In this code chan-name->id is supposed to be a map, but it can also be `nil`.

``` clojure
(defn channel-days [db chan-name]
(let [{:keys [chan-day-cnt chan-name->id]} @!indexes]
(some->> chan-name
chan-name->id
chan-day-cnt
(sort-by first reverse-compare))))
```

The solution can be as simple as putting some placeholder maps in `!indexes`

``` clojure
(defonce !indexes (atom {:chan-name->id {} ,,,}))
```

Find the channel-days function and the !indexes definition described in the issue, then trace how the indexer populates the lookup maps. Ensure the unpopulated index state produces empty pages or a waiting state instead of a NullPointerException, and verify the affected page behavior during startup.

Written by the indexing model from the issue text.