fix(geometry/rwr): Fix missing pads due to buggy `add_to_compound`

The origin of this bug was found via git-bisect, commit
d6fe67a373
is buggy, which switches from GeometryWithRtree to RecordingGeometryWithRtree.

In PR #128, it was discovered that `add_to_compound` appears to
be missing the part that actually invokes the function that performs
the underlying action that is supposed to be diffed.

Fixes #127

src/geometry/recording_with_rtree.rs

@@ -149,7 +149,7 @@ impl<
         let old_members = geometry.compound_members(compound).collect();
         let old_weight = geometry.compound_weight(compound);
 
-        // TODO ???
+        self.geometry_with_rtree.add_to_compound(primitive, compound);
 
         let geometry = self.geometry_with_rtree.geometry();
         let new_members = geometry.compound_members(compound).collect();