Custom primitive object inspectors in the Serde need to override getPrimitiveJavaObject also

This fixes https://github.com/rcongiu/Hive-JSON-Serde/issues/67

From `org.apache.hadoop.hive.ql.udf.generic.GenericUDAFMax.GenericUDAFMaxEvaluator#merge`

The aggregation buffer is being initialized here and the object inspector we have here is from the Serde. And in these primitiveObjectInspectors, getPrimitiveJavaObject hasn't been overridden.

```java
        if (myagg.o == null || r < 0) {
          myagg.o = ObjectInspectorUtils.copyToStandardObject(partial, inputOI,
              ObjectInspectorCopyOption.JAVA);
        }
```