Function bounding_rect_single 

pub fn bounding_rect_single(
    vs: &mut dyn VertexSource,
    path_id: u32,
) -> Option<RectD>

Compute the bounding rectangle of a single path from a vertex source.

Rewinds the vertex source to path_id, iterates all vertices, and returns the axis-aligned bounding box. Returns None if no vertices are found.

Port of C++ agg::bounding_rect_single.