```
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
{
        const auto * from_low_cardinality = typeid_cast<const DataTypeLowCardinality *>(from_type.get());
        const auto * to_low_cardinality = typeid_cast<const DataTypeLowCardinality *>(to_type.get());
        const auto & from_nested = from_low_cardinality ? from_low_cardinality->getDictionaryType() : from_type;
        const auto & to_nested = to_low_cardinality ? to_low_cardinality->getDictionaryType() : to_type;
        if (from_type->onlyNull())
        {
            if (!to_nested->isNullable())
            {
                if (cast_type == CastType::accurateOrNull)
                {
                    return createToNullableColumnWrapper();
                }
                else
                {
                    throw Exception{"Cannot convert NULL to a non-nullable type", ErrorCodes::CANNOT_CONVERT_TYPE};
                }
            }
            return [](ColumnsWithTypeAndName &, const DataTypePtr & result_type, const ColumnNullable *, size_t input_rows_count)
            {
                return result_type->createColumnConstWithDefaultValue(input_rows_count)->convertToFullColumnIfConst();
            };
        }
        bool skip_not_null_check = false;
        if (from_low_cardinality && from_nested->isNullable() && !to_nested->isNullable())
            
            skip_not_null_check = true;