Fix spacing in pretty printed PatKind::Struct with no fields

[dtolnay]

Follow-up to #92238 fixing one of the FIXMEs.

macro_rules! repro {
    ($pat:pat) => {
        stringify!($pat)
    };
}

fn main() {
    println!("{}", repro!(Struct {}));
}

Before: Struct {  }
After: Struct {}

[rust-highfive]

r? @michaelwoerister

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[michaelwoerister]

Looks good to me, thanks @dtolnay!

@bors r+ rollup

[bors]

📌 Commit 8d7cf1a has been approved by michaelwoerister