Hello,

so I'm working to integrate CatBoost model with our ClickHouse cluster. It appears that, whenever we create a new XML model file in the configured path, the **first** call to the new model never returns (this is true both of the HTTP interface as well as via clickhouse-client).

Independently from whether the locked statement gets cancelled, subsequent calls succeed immediately.

```
16e8bdb5bbb9 :) select version();

SELECT version()

┌─version()─┐
│ 20.6.3.28 │
└───────────┘

1 rows in set. Elapsed: 0.006 sec.
```

Is this known behavior? If it helps, my models look like this:

```
<models>
    <model>
        <type>catboost</type>
        <name>ctr_predictor</name>
        <path>/catboost/my_predictor</path>
        <lifetime>0</lifetime>
    </model>
</models>
```
const CreateObjectFunction & create_object_function_,
        const String & type_name_,
        Poco::Logger * log_)
        : create_object(create_object_function_)
        , type_name(type_name_)
        , log(log_)
    {
    }
    ~LoadingDispatcher()
    {
        std::unique_lock lock{mutex};
        infos.clear(); 
        
        while (!loading_threads.empty())
        {
            auto it = loading_threads.begin();
            auto thread = std::move(it->second);
            loading_threads.erase(it);
            lock.unlock();
            event.notify_all();
            thread.join();
            lock.lock();
        }
    }
    using ObjectConfigsPtr = LoadablesConfigReader::ObjectConfigsPtr;
    
    void setConfiguration(const ObjectConfigsPtr & new_configs)