After you create table with fields with dots and after alter table clickhouse throw exception about bad cast
version 20.12.3

How to reproduce

```
CREATE TABLE test_nested
(
    `id` String,
    `with_dot.str` String,
    `with_dot.array` Array(Int32)
)
ENGINE = MergeTree()
ORDER BY id


Insert Into test_nested (id,`with_dot.str`, `with_dot.array`) VALUES('123','asd',[1,2])

select * FROM test_nested


SELECT *
FROM test_nested

Query id: 42f26a6e-7573-4169-a4a1-9fe7022ba656

┌─id──┬─with_dot.str─┬─with_dot.array─┐
│ 123 │ asd          │ [1,2]          │
└─────┴──────────────┴────────────────┘

alter table test_nested ADD COLUMN `with_dot.bool` UInt8


SELECT *
FROM test_nested

Query id: 3ea8ae6b-1e0a-4ae5-b4d0-dcdcb6b7b8f8


Received exception from server (version 20.12.3):
Code: 49. DB::Exception: Received from localhost:9000. DB::Exception: Bad cast from type DB::DataTypeNumber<char8_t> to DB::DataTypeArray: (while reading from part /var/lib/clickhouse/store...
```

I think that happend because clickhouse after altert think that field `with_dot.bool` is nested and trying to cast to array, but i'm not creating nested field, i'm only use field name with `.`

{
    auto name_in_storage = required_column.getNameInStorage();
    ColumnsFromPart::ConstLookupResult it;
    if (alter_conversions.isColumnRenamed(name_in_storage))
    {
        String old_name = alter_conversions.getColumnOldName(name_in_storage);
        it = columns_from_part.find(old_name);
    }
    else
    {
        it = columns_from_part.find(name_in_storage);
    }
    if (it == columns_from_part.end())
        return required_column;
    const DataTypePtr & type = *it->getMapped();
    if (required_column.isSubcolumn())
    {
        auto subcolumn_name = required_column.getSubcolumnName();
        auto subcolumn_type = type->tryGetSubcolumnType(subcolumn_name);
        if (!subcolumn_type)
            return required_column;
        return {String(it->getKey()), subcolumn_name, type, subcolumn_type};
    }
    return {String(it->getKey()), type};
}
void IMergeTreeReader::performRequiredConversions(Columns & res_columns)