set some refs to nukk

Author: codeanticode

core/src/processing/core/PGraphics.java

@@ -719,6 +719,7 @@ protected void allocate() { }
    * endRaw(), in order to shut things off.
    */
   public void dispose() {  // ignore
+    parent = null;
   }
 
 

core/src/processing/opengl/PGL.java

@@ -408,6 +408,8 @@ public PGL(PGraphicsOpenGL pg) {
 
 
   public void dispose() {
+    graphics = null;
+    sketch = null;
     destroyFBOLayer();
   }