[SPARK-25760][SQL] Set AddJarCommand return empty

## What changes were proposed in this pull request?

Only `AddJarCommand` return `0`, the user will be confused about what it means. This PR sets it to empty.

```sql
spark-sql> add jar /Users/yumwang/spark/sql/hive/src/test/resources/TestUDTF.jar;
ADD JAR /Users/yumwang/spark/sql/hive/src/test/resources/TestUDTF.jar
0
spark-sql>
```

## How was this patch tested?

manual tests
```sql
spark-sql> add jar /Users/yumwang/spark/sql/hive/src/test/resources/TestUDTF.jar;
ADD JAR /Users/yumwang/spark/sql/hive/src/test/resources/TestUDTF.jar
spark-sql>
```

Closes #22747 from wangyum/AddJarCommand.

Authored-by: Yuming Wang <yumwang@ebay.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: wangyum

sql/core/src/main/scala/org/apache/spark/sql/execution/command/resources.scala

@@ -38,7 +38,7 @@ case class AddJarCommand(path: String) extends RunnableCommand {
 
   override def run(sparkSession: SparkSession): Seq[Row] = {
     sparkSession.sessionState.resourceLoader.addJar(path)
-    Seq(Row(0))
+    Seq.empty[Row]
   }
 }