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>
```
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template <typename ReturnType, typename>
ReturnType ExternalLoader::load(const String & name) const
{
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}
template <typename ReturnType, typename>
ReturnType ExternalLoader::load(const FilterByNameFunction & filter) const
{
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}
template <typename ReturnType, typename>
ReturnType ExternalLoader::loadOrReload(const String & name) const
{
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    auto result = loading_dispatcher->tryLoadOrReload<LoadResult>(name, WAIT);
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}
template <typename ReturnType, typename>
ReturnType ExternalLoader::loadOrReload(const FilterByNameFunction & filter) const