Fix crash in ImageProcessing blend test

The blend test would use a stale context
when running all tests.

bug 7327728

Change-Id: I5802b9b382d8893419efe86d33fdfeeb27729e31

Author: Jason Sams

tests/RenderScriptTests/ImageProcessing/src/com/android/rs/image/Blend.java

@@ -52,8 +52,10 @@ public class Blend extends TestBase {
             new AdapterView.OnItemSelectedListener() {
                 public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
                     currentIntrinsic = pos;
-                    runTest();
-                    act.updateDisplay();
+                    if (mRS != null) {
+                        runTest();
+                        act.updateDisplay();
+                    }
                 }
 
                 public void onNothingSelected(AdapterView parent) {

tests/RenderScriptTests/ImageProcessing/src/com/android/rs/image/TestBase.java

@@ -123,6 +123,7 @@ public void finish() {
 
     public void destroy() {
         mRS.destroy();
+        mRS = null;
     }
 
     public void updateBitmap(Bitmap b) {