make Allocation.destroy() include setSurface(null) for USAGE_IO_OUTPUT

(Native RS)

Change-Id: I23041da03c2c928ceec76037804abb5dc7e6eb64

rs/java/android/renderscript/Allocation.java

@@ -1878,4 +1878,15 @@ public class Allocation extends BaseObj {
         }
     }
 
+    /**
+     * For USAGE_IO_OUTPUT, destroy() implies setSurface(null).
+     *
+     */
+    @Override
+    public void destroy() {
+        if((mUsage & USAGE_IO_OUTPUT) != 0) {
+            setSurface(null);
+        }
+        super.destroy();
+    }
 }