rune fmt breaks multiline comments

[SWW13]

error.rn:

pub fn main() {
    /*
    test
    */
}

$ cargo install rune-cli --version 0.13.2
$ rune fmt error.rn
$ cat error.rn
pub fn main() {
/*
    test    *
}

I have experienced the issue of disappearing lines for a while now and just now triaged the source, so it may be related to the changes in #527 / #539.
I further tracked it down, it was already present in 0.13.0, the initial commit 802101c9 returned a parser error for the file:

$ cargo +1.74.0 run --bin rune -- fmt test.rn
!! error.rn: error while parsing source
0 unchanged
0 succeeded
1 failed