HeightfieldCollisionShape is invisible in jme3-jbullet with setDebugEnabled()

Physics debug visualization works for HeightfieldCollisionShape in jme3-bullet but not in jme3-jbullet.

To demonstrate this issue, modify jme3test.terrain.TerrainGridAlphaMapTest as follows:

@@ -47,7 +47,7 @@
     private float grassScale = 64;
     private float dirtScale = 16;
     private float rockScale = 128;
-    private boolean usePhysics = false;
+    private boolean usePhysics = true;
 
     public static void main(final String[] args) {
         TerrainGridAlphaMapTest app = new TerrainGridAlphaMapTest();
@@ -161,6 +161,7 @@
         this.terrain.addControl(control);
 
         final BulletAppState bulletAppState = new BulletAppState();
+        bulletAppState.setDebugEnabled(true);
         stateManager.attach(bulletAppState);

With jme3-bullet, the HeightfieldCollisionShape is visualized as blue wireframe, overlaid on the grass/dirt/rock. With jme3-jbullet, only the grass/dirt/rock is visible.

Start with jme3test.terrain.TerrainGridAlphaMapTest, enabling physics and setDebugEnabled(true) as shown. Compare the HeightfieldCollisionShape debug visualization in jme3-bullet and jme3-jbullet, then trace the respective debug-rendering entry points. Done means jme3-jbullet displays the heightfield as a blue wireframe over the terrain.