Some layouts return more rects than windows

[hertg]

Found the issue while testing in a MainAndStack like layout that may have multiple main windows but only one window is provided.

Layout {
    name: "MultiMain".to_string(),
    columns: Columns {
        main: Some(crate::layouts::Main {
            count: 2,
            ..Default::default()
        }),
        ..Default::default()
    },
    ..Default::default()
}

Using this layout with a single window should return just one Rect, not two.