Format `Struct { .. }` on one line even with `{:#?}`.
The result of `debug_struct("A").finish_non_exhaustive()` before this change:
```
A {
..
}
```
And after this change:
```
A { .. }
```
If there's any fields, the result stays unchanged:
```
A {
field: value,
..
}
|
||
|---|---|---|
| .. | ||
| rt | ||
| builders.rs | ||
| float.rs | ||
| mod.rs | ||
| num.rs | ||