load data will panic if the content is break at escape character

[xiongjiwei]

Bug Report

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1. Minimal reproduce step (Required)

tidb/executor/load_data.go

Lines 550 to 568 in 79171be

	nextDataIdx := curStartIdx + endIdx + terminatedLen
	if len(prevData) == 0 {
	return curData[curStartIdx : curStartIdx+endIdx], curData[nextDataIdx:], true
	}
	// terminated symbol in the curData
	prevData = append(prevData, curData[:nextDataIdx]...)
	if ignore {
	endIdx = strings.Index(string(hack.String(prevData[startingLen:])), e.LinesInfo.Terminated)
	} else {
	endIdx = e.IndexOfTerminator(prevData[startingLen:], inquotor)
	}
	if endIdx >= prevLen {
	return prevData[startingLen : startingLen+endIdx], curData[nextDataIdx:], true
	}
	// terminated symbol in the middle of prevData and curData
	lineLen := startingLen + endIdx + terminatedLen
	return prevData[startingLen : startingLen+endIdx], curData[lineLen-prevLen:], true

if data is broken at escape character and then followed by a \n, then it will get the wrong index of the new line, it will cause panic

[github-actions]

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