[RenderScript] Fail with Exception from validateObjectIsPrimitiveArray

Bug: http://b/25982676

Instead of returning null from validateObjectIsPrimitiveArray, fail with
an exception.  The callers of this function do not check for null.

Change-Id: Idd2b50a7b137e8d2db7a334bb9a48c1b19ee2403

rs/java/android/renderscript/Allocation.java

@@ -142,7 +142,10 @@ public class Allocation extends BaseObj {
             }
             return Element.DataType.FLOAT_64;
         }
-        return null;
+
+        throw new RSIllegalArgumentException("Parameter of type " + cmp.getSimpleName() +
+            "[] is not compatible with data type " + mType.mElement.mType.name() +
+            " of allocation");
     }