[bug] automatic fmt is not run for invisible buffers

[VuiMuich]

As far as my search on github and my question on the matrix chat went, this has not been reported yet.

Reproduction steps

Here is a minimal Rust code example. Just create a new cargo crate with cargo init test_helix_auto_fmt and place the following example in its src/main.rs:

/* For easiest demonstration simply collapse the file to a single line with `%J` */
fn main() {
    let editor = String::from("Helix");
    print!(
        "This is a one line minimal example to show, how {2} {}{}",
        "does not run automatic 'fmt' when the ", "buffer is not visible in any window.", editor
    );
    return;
}
// Then open a scratch buffer with `:n` and run `:xa!`
// Observe changes to this file have been written but it hadn't been treated by `fmt`.

Then follow the instructions in the comments.

Environment

• Platform: Manjaro Linux (should be irrelevant though)
• Helix version: helix v0.5.0-342-gbd0d20a

Expected behaviour

If helix is configured to run fmt on every file write it should be applied to any file that can be written to disk, despite the visibility of its buffer.