Merge change 22186 into eclair

* changes:
  Allow null to be re-bound as a root script.  This was always legal from native and just a limitation of the java binding for the API.

graphics/java/android/renderscript/RenderScript.java

@@ -281,7 +281,11 @@ public class RenderScript {
     // Root state
 
     public void contextBindRootScript(Script s) {
-        nContextBindRootScript(s.mID);
+        int id = 0;
+        if(s != null) {
+            id = s.mID;
+        }
+        nContextBindRootScript(id);
     }
 
     //public void contextBindSampler(Sampler s, int slot) {