Return Option from Geometry::of_curve

This makes the method more flexible and error messages about missing
curve geometry more targetted.

crates/fj-core/src/geometry/geometry.rs

@@ -108,10 +108,8 @@ impl Geometry {
     /// ## Panics
     ///
     /// Panics, if the geometry of the curve is not defined.
-    pub fn of_curve(&self, curve: &Handle<Curve>) -> &CurveGeom {
-        self.curve
-            .get(curve)
-            .expect("Expected geometry of half-edge to be defined")
+    pub fn of_curve(&self, curve: &Handle<Curve>) -> Option<&CurveGeom> {
+        self.curve.get(curve)
     }
 
     /// # Access the geometry of the provided half-edge

crates/fj-core/src/operations/build/half_edge.rs

@@ -133,6 +133,7 @@ pub trait BuildHalfEdge {
                     .layers
                     .geometry
                     .of_curve(half_edge.curve())
+                    .expect("Curve geometry was just defined in same function")
                     .local_on(&surface)
                     .path,
                 boundary: boundary.unwrap_or_default(),

crates/fj-core/src/operations/build/shell.rs

@@ -107,6 +107,10 @@ pub trait BuildShell {
                                             .layers
                                             .geometry
                                             .of_curve(&curve)
+                                            .expect(
+                                                "Curve geometry was just \
+                                                defined in same function",
+                                            )
                                             .local_on(&surface)
                                             .path,
                                         boundary,