edge.controlPoints() is undefined for edges between a parent node a…

…nd one of its descendants. While these edges aren't strictly loops, they are displayed in a similar way to loops using two beziers.

Ref : `edge.controlPoints()` is `undefined` for loops #2139

src/extensions/renderer/base/coord-ele-math/edge-control-points.js

@@ -786,7 +786,7 @@ BRp.getControlPoints = function( edge ){
   let rs = edge[0]._private.rscratch;
   let type = rs.edgeType;
 
-  if( type === 'bezier' || type === 'multibezier' || type === 'self' ){
+  if( type === 'bezier' || type === 'multibezier' || type === 'self' || type === 'compound' ){
     return getPts( rs.ctrlpts );
   }
 };