Copy rough set index Data in a wrong way

[Lloyd-Pottiger]

Bug Report

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tiflash/dbms/src/Storages/DeltaMerge/Index/MinMaxIndex.cpp

Lines 307 to 311 in ec00c9a

	// todo use StringRef instead of String
	auto min = String(chars[prev_offset], offsets[pos] - prev_offset - 1);
	pos = i * 2 + 1;
	prev_offset = offsets[pos - 1];
	auto max = String(chars[prev_offset], offsets[pos] - prev_offset - 1);

When using String, we should use reinterpret_cast<const char *>(&chars[prev_offset]) instead of chars[prev_offset], so that it will call constructor constexpr basic_string( const CharT* s, const Allocator& alloc = Allocator()) rather than constexpr basic_string( size_type count, CharT ch, const Allocator& alloc = Allocator() );

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[JaySon-Huang]

the issue is fixed in the master branch by #8298