[SQL] enable empty aggr test case

This is fixed by SPARK-4318 #3184

Author: Daoyuan Wang <daoyuan.wang@intel.com>

Closes #3445 from adrian-wang/emptyaggr and squashes the following commits:

982575e [Daoyuan Wang] enable empty aggr test case

sql/hive/src/test/resources/golden/empty aggregate input-0-bbd21aa0c1faf4c1fe6d8a822b416349

+NULL

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveQuerySuite.scala

@@ -319,10 +319,8 @@ class HiveQuerySuite extends HiveComparisonTest with BeforeAndAfter {
   createQueryTest("DISTINCT",
     "SELECT DISTINCT key, value FROM src")
 
-  ignore("empty aggregate input") {
-    createQueryTest("empty aggregate input",
-      "SELECT SUM(key) FROM (SELECT * FROM src LIMIT 0) a")
-  }
+  createQueryTest("empty aggregate input",
+    "SELECT SUM(key) FROM (SELECT * FROM src LIMIT 0) a")
 
   createQueryTest("lateral view1",
     "SELECT tbl.* FROM src LATERAL VIEW explode(array(1,2)) tbl as a")