Panic in the TestVerifyChecksum

[hawkingrei]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

2. What did you expect to see? (Required)

3. What did you see instead (Required)

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x7df2d15]
goroutine 33670 [running]:
github.com/pingcap/tidb/pkg/distsql.(*selectResult).Close(0xc009ae8380)
	pkg/distsql/select_result.go:610 +0x175
github.com/pingcap/tidb/pkg/executor.(*ChecksumTableExec).handleChecksumRequest.func1()
	pkg/executor/checksum.go:159 +0x29
github.com/pingcap/tidb/pkg/executor.(*ChecksumTableExec).handleChecksumRequest(0xc0063f8960, 0xc008f6aa80?)
	pkg/executor/checksum.go:170 +0x3e5
github.com/pingcap/tidb/pkg/executor.(*ChecksumTableExec).checksumWorker(0xc00a23cc40?, 0xc0000324d0?, 0xc007bb6fb0?)
	pkg/executor/checksum.go:144 +0xa7
created by github.com/pingcap/tidb/pkg/executor.(*ChecksumTableExec).Open in goroutine 223
	pkg/executor/checksum.go:64 +0x105
================================================================================

https://tiprow.hawkingrei.com/view/gs/pingcapprow/pr-logs/pull/pingcap_tidb/51916/fast_test_tiprow/1770373340058357760#1:build-log.txt%3A2591

4. What is your TiDB version? (Required)

[D3Hunter]

same root cause as this #51928, Introduced by #51787.