FIRST accumulator gives wrong result when fed with multiple batches

[mustafasrepo]

Describe the bug

First Accumulator in its current implementation is not aware of whether it is set or not. Hence when fed with multiple batches, it returns first value of the last batch.

To Reproduce

One can use test below to reproduce problem

#[tokio::test]
async fn test_first_value_multi_partition() -> Result<()> {
    let config = SessionConfig::new()
        .with_target_partitions(1);
    let ctx = SessionContext::with_config(config);
    let fields = vec![Field::new("a", DataType::Int64, false)];
    let schema = Arc::new(Schema::new(fields));
    let batch1 = RecordBatch::try_new(schema.clone(), vec![Arc::new(Int64Array::from(vec![1,2,3,4])) as ArrayRef])?;
    let batch2 = RecordBatch::try_new(schema.clone(), vec![Arc::new(Int64Array::from(vec![5,6,7,8])) as ArrayRef])?;
    let partitions = vec![vec![batch1, batch2]];
    let mem_table = MemTable::try_new(schema, partitions)?;
    ctx.register_table("table1", Arc::new(mem_table))?;

    let sql = "SELECT FIRST_VALUE(a)
                    FROM table1";

    let msg = format!("Creating logical plan for '{sql}'");
    let dataframe = ctx.sql(sql).await.expect(&msg);
    let physical_plan = dataframe.create_physical_plan().await?;
    let batches = collect(physical_plan, ctx.task_ctx()).await?;
    print_batches(&batches)?;
    Ok(())
}

result should be 1 (first value of the first batch), where as now it returns 5(first_value of the last batch).

Expected behavior

Above test should return 1

Additional context

No response