Add Java exceptions to catch RS calls with no context or no surface.
diff --git a/graphics/java/android/renderscript/Sampler.java b/graphics/java/android/renderscript/Sampler.java
index 5e0b110..625a576 100644
--- a/graphics/java/android/renderscript/Sampler.java
+++ b/graphics/java/android/renderscript/Sampler.java
@@ -100,6 +100,7 @@
         }
 
         public Sampler create() {
+            mRS.validate();
             return internalCreate(mRS, this);
         }
     }