[SPARK-17849][SQL] Fix NPE problem when using grouping sets

## What changes were proposed in this pull request?

Prior this pr, the following code would cause an NPE:
`case class point(a:String, b:String, c:String, d: Int)`

`val data = Seq(
point("1","2","3", 1),
point("4","5","6", 1),
point("7","8","9", 1)
)`
`sc.parallelize(data).toDF().registerTempTable("table")`
`spark.sql("select a, b, c, count(d) from table group by a, b, c GROUPING SETS ((a)) ").show()`

The reason is that when the grouping_id() behavior was changed in #10677, some code (which should be changed) was left out.

Take the above code for example, prior #10677, the bit mask for set "(a)" was `001`, while after #10677 the bit mask was changed to `011`. However, the `nonNullBitmask` was not changed accordingly.

This pr will fix this problem.
## How was this patch tested?

add integration tests

Author: wangyang <wangyang@haizhi.com>

Closes #15416 from yangw1234/groupingid.

(cherry picked from commit fb0d6081)
Signed-off-by: Herman van Hovell <hvanhovell@databricks.com>