Importers: a brush that draws itself by name no longer crashes

A scatter brush whose art is an instance of a symbol stroked with that brush, or any brush whose
art is painted with a pattern whose tile is stroked with it, drew itself without end: a stack
overflow in a hand-written native file. Brush pieces already strip the brushes of their own
strokes; now what they draw by name that would draw a brushed stroke (a symbol instance, or a
pattern paint, also through the symbols and patterns those use) is left out too, in one place
(`stroke_pieces`, which every renderer and exporter calls with the document).

Probed the rest of item 2 of the depth follow-up with hand-written hostile inputs, kept as tests:
graph designs of deep art and of a symbol holding itself, Affinity groups nested to and past
both of its reader's caps, DXF blocks inserting themselves, EMF/WMF saving states without end,
and plug-in manifests and output nested 30,000 to 100,000 deep. None of them overflowed.

crates/engine/src/cmd/pathops.rs

@@ -594,7 +594,7 @@ pub(crate) fn outlined_stroke(
     st: &StrokeLayer,
 ) -> Option<Node> {
     if let Some(b) = st.brush.as_deref().and_then(|name| brushes.iter().find(|b| b.name == name)) {
-        let mut pieces = vectorcraft_brush::stroke_pieces(b, &path.to_bezpath(), st);
+        let mut pieces = vectorcraft_brush::stroke_pieces(d, b, &path.to_bezpath(), st);
         let art = match pieces.len() {
             0 => return None,
             1 => pieces.remove(0),