Asset loading doesn't update correctly when using `WinitSettings::desktop_app()`

## Bevy version

0.8.1

## What you did

Ran the ui example and didn't touch the mouse when it started up

## What went wrong

The bevy logo doesn't show up instantly. It only appears when you move the mouse.

## Additional information

This is caused by the use of `WinitSettings::desktop_app()` in this example. Essentially, the issue is that it makes it only update when it detects user input or every 5 seconds. This means the asset_server doesn't update for the first 5 seconds and any asset that wasn't instantly loaded won't display until the first user input is detected.