AssetServer load_folder gives AssetFolderNotADirectory when it definitely is

## Bevy version

0.7.0 from crates.io

## What you did

```
struct SpriteHandles(Vec);

fn load_textures(mut sprite_handles: ResMut, assets: Res) {
info!("Loading textures...");
sprite_handles.0 = assets.load_folder(".")
.expect("Failed to load textures");
}
```

## What went wrong

```
2022-07-13T12:08:14.321073Z INFO client: Loading textures...
thread 'main' panicked at 'Failed to load textures: AssetFolderNotADirectory(".")', client/src/main.rs:80:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

- expected it to load anything, probably more than it should
- errored out even though the currently directory does indeed exist

## Additional information

havent touched any asset server stuff in this project