```
SELECT
    CAST(([2, 1, 1023], ['', '']), 'Map(UInt8, String)') AS map,
    map[10]
```

Triggers `Assertion 'n < size()' failed` in `DB::ColumnString::operator[](unsigned long)`
https://clickhouse-test-reports.s3.yandex.net/18481/64c4ade5b0e0c9a13d6c2475431daf431fc97554/fuzzer/fuzzer.log

Introduced here: #17829
First found here: #18481
throw Exception("Illegal column " + col_from->getName()
                + " of first argument of function " + Name::name,
                ErrorCodes::ILLEGAL_COLUMN);
        if (std::is_same_v<FromDataType, DataTypeFixedString> && !col_from_fixed_string)
            throw Exception("Illegal column " + col_from->getName()
                + " of first argument of function " + Name::name,
                ErrorCodes::ILLEGAL_COLUMN);
        size_t size = input_rows_count;
        typename ColVecTo::MutablePtr col_to = nullptr;
        if constexpr (IsDataTypeDecimal<ToDataType>)
        {
            UInt32 scale = additions;
            if constexpr (to_datetime64)
            {
                ToDataType check_bounds_in_ctor(scale, local_time_zone ? local_time_zone->getTimeZone() : String{});
            }
            else
            {
                ToDataType check_bounds_in_ctor(ToDataType::maxPrecision(), scale);
            }
            col_to = ColVecTo::create(size, scale);
        }
        else
            col_to = ColVecTo::create(size);
        typename ColVecTo::Container & vec_to = col_to->getData();
        ColumnUInt8::MutablePtr col_null_map_to;
        ColumnUInt8::Container * vec_null_map_to [[maybe_unused]] = nullptr;
        if constexpr (exception_mode == ConvertFromStringExceptionMode::Null)
        {
            col_null_map_to = ColumnUInt8::create(size);