[BUG] Plotting very slow when using multiple plots.

[ErikbStorm]

When using plotters the plots get generated extemely fast when not using multiple plots. But when I add a single split into the root, generating a single plot will take around 2 seconds to create, whereas before it was done in milliseconds.

let root_area = BitMapBackend::new(OUT_FILE_NAME, (IMAGE_WIDTH, IMAGE_HEIGHT)).into_drawing_area();
   
// this will cause the presenting of the plot to be 1000x slower.
let (upper, lower) = root_area.split_vertically(50.percent());

Using the latest verison.