This commit attempts to fix the case where the messages loaded initially don't fill the screen. It would prevent user to scroll and as a result to load more.
There are multiple fixes in this commit:
- the main fix is removing this code which was preventing the actual fill:
```javascript
// prevents an edge case where user clicks bottom arrow
// just after scrolling to top
if (loadingPast && this.#isAtBottom()) {
return;
}
```
- ensures we always give a page site to the `chatApi.channel(...)` call if we have one, in the current state when `fetchFromLastRead` was `true` we would not set `args.page_size`
- ensures the `query_paginated_messages` is having a valid page size, which is not nil and not > `MAX_PAGE_SIZE`
- write a spec for the autofill, it was a challenging spec to write but it should give us the confidence we need here
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