statistics: kill in time when to mergeGlobalTopN with partition

Signed-off-by: Weizhen Wang <wangweizhen@pingcap.com>

statistics/cmsketch.go

@@ -834,6 +834,9 @@ func MergePartTopN2GlobalTopN(loc *time.Location, version int, topNs []*TopN, n
 			// 1. Check the topN first.
 			// 2. If the topN doesn't contain the value corresponding to encodedVal. We should check the histogram.
 			for j := 0; j < partNum; j++ {
+				if atomic.LoadUint32(kiiled) == 1 {
+					return nil, nil, nil, errors.Trace(ErrQueryInterrupted)
+				}
 				if (j == i && version >= 2) || topNs[j].findTopN(val.Encoded) != -1 {
 					continue
 				}