**Describe the bug**

I have a table like:

```
CREATE TABLE test (
    time DateTime64(3)
    ...
) ENGINE = MergeTree()
PARTITION BY toStartOfInterval(time, INTERVAL 1 HOUR)
...
```

But when I search in `system.parts` it does not appear to have the `min/max` columns appropriately set?

```
partition:                             2020-06-01 01:00:00
min_date:                              1970-01-01
max_date:                              1970-01-01
min_time:                              1970-01-01 00:00:00
max_time:                              1970-01-01 00:00:00
```

I assume that if these were correctly set, doing a `select toStartOfInterval(time, interval 1 day), count()` type query would be pretty instant rather than trying to scan everything? I am guessing this is due to the `DateTime64` type in use?

Clickhouse 20.11.3.3

{
    auto metadata_snapshot = data.getInMemoryMetadataPtr();
    const auto & partition_key = metadata_snapshot->getPartitionKey();
    auto minmax_column_names = data.getMinMaxColumnsNames(partition_key);
    auto minmax_column_types = data.getMinMaxColumnsTypes(partition_key);
    size_t minmax_idx_size = minmax_column_types.size();
    hyperrectangle.reserve(minmax_idx_size);
    for (size_t i = 0; i < minmax_idx_size; ++i)
    {
        String file_name = part_path + "minmax_" + escapeForFileName(minmax_column_names[i]) + ".idx";
        auto file = openForReading(disk_, file_name);
        const DataTypePtr & data_type = minmax_column_types[i];
        Field min_val;
        data_type->deserializeBinary(min_val, *file);
        Field max_val;
        data_type->deserializeBinary(max_val, *file);
        hyperrectangle.emplace_back(min_val, true, max_val, true);
    }
    initialized = true;
}
void IMergeTreeDataPart::MinMaxIndex::store(
    const MergeTreeData & data, const DiskPtr & disk_, const String & part_path, Checksums & out_checksums) const
{
    auto metadata_snapshot = data.getInMemoryMetadataPtr();
    const auto & partition_key = metadata_snapshot->getPartitionKey();
    auto minmax_column_names = data.getMinMaxColumnsNames(partition_key);
    auto minmax_column_types = data.getMinMaxColumnsTypes(partition_key);
    store(minmax_column_names, minmax_column_types, disk_, part_path, out_checksums);
}
void IMergeTreeDataPart::MinMaxIndex::store(