Return empty value when select count(*) from empty table with extra RePartition after it

[jackylee-ch]

Describe the bug When there is a ShuffleExchange after HashAgg, whose agg func is Count, and there are no inputs passed to HashAgg, gazelle will return empty batch rather than return none empty batch with 0.

To Reproduce

spark.sql("select 1 as a").filter("a > 1").groupBy().count().repartition(10).explain(true)

[jackylee-ch]

The main reason for this problem is the iterator defined in ColumnarHashAggregateExec is invalid. Its hasNext would return different value if we called it twice without calling next func. And in ColumnarShuffleWriteExec, we would check hasNext twice before calling next.