FIRST/LAST returns wrong result with `PartialMerge`

[comphead]

Describe the bug

Found in #4003

Steps to reproduce

test("partialMerge - FIRST/LAST with distinct aggregates falls back") {
    val numValues = 10000
    Seq(100).foreach { numGroups =>
      Seq(128).foreach { batchSize =>
        withSQLConf(
          SQLConf.COALESCE_PARTITIONS_ENABLED.key -> "true",
          CometConf.COMET_BATCH_SIZE.key -> batchSize.toString) {
          withParquetTable(
            (0 until numValues).map(i => (i, Random.nextInt() % numGroups)),
            "tbl",
            false) {
            withView("v") {
              sql("CREATE TEMP VIEW v AS SELECT _1, _2 FROM tbl ORDER BY _1")
              checkSparkAnswerAndOperator(
                "SELECT _2, FIRST(_1), LAST(_1), COUNT(DISTINCT _1)" +
                  " FROM v GROUP BY _2 ORDER BY 1, 2, 3, 4")
            }
          }
        }
      }
    }
  }

== Results ==
!== Spark Answer - 199 ==                                              == Comet Answer - 199 ==
 struct<_2:int,first(_1):int,last(_1):int,count(DISTINCT _1):bigint>   struct<_2:int,first(_1):int,last(_1):int,count(DISTINCT _1):bigint>
![-99,169,9603,61]                                                     [-99,169,9804,61]
![-98,307,9492,48]                                                     [-98,307,9870,48]
![-97,153,9197,47]                                                     [-97,153,9175,47]
![-96,571,9486,56]                                                     [-96,571,9762,56]
![-95,243,9720,50]                                                     [-95,243,9642,50]
 [-94,234,9747,45]                                                     [-94,234,9747,45]
![-93,637,9020,45]                                                     [-93,637,9515,45]
 [-92,13,9754,51]                                                      [-92,13,9754,51]
![-91,75,9643,47]                                                      [-91,75,9872,47]
![-90,106,9971,50]                                                     [-90,106,9911,50]
 [-89,323,9937,49]                                                     [-89,323,9937,49]
![-88,49,9577,43]                                                      [-88,49,9756,43]
![-87,134,9960,45]                                                     [-87,134,9998,45]
![-86,12,9180,47]                                                      [-86,12,9607,47]
![-85,220,9565,58]                                                     [-85,220,9533,58]
![-84,815,9734,48]                                                     [-84,815,9919,48]

Expected behavior

Should return correct values

Additional context

No response