Fix bug in helix.visible

Author: BruceSherwood

lib/glow/primitives.js

@@ -264,6 +264,7 @@
             set: function(value) {
                 if (value == (this.__id != null)) return
                 if (this.__comp) this.__comp.visible = value // extrusion and ring use a compound
+                if (this.__curve) this.__curve.visible = value
                 if (value) {
                     this.__id = nextVisibleId
                     nextVisibleId++