Location list stays open when empty

## Information

**VIM version**

```
NVIM v0.4.3
Build type: Release
```

PlugUpdate shows `- ale: Already up to date. `

Operating System: Arch linux

## What went wrong

Whenever I write some python code and flake8 stop a linting error, saving the file will have black auto-fix the issue. I'm expecting `:lclose` to be auto-executed because the location list is now empty, but the location list stays open

Related to #2460.

## Reproducing the bug

```vim
let g:ale_fixers = {
\ '*': ['remove_trailing_lines', 'trim_whitespace'],
\ 'python': ['black'],
\ }
let g:ale_linters = {
\ 'python': ['flake8'],
\}
```

### :ALEInfo

https://gist.github.com/AdrienLemaire/7b37ed6386d1419c0d9799908a1edd78