When I queried `system.metrics` table, I found some negative values which hint to some potential internal overflows.

```
SELECT *
FROM system.metrics
FORMAT Vertical

...

Row 31:
───────
metric:      MemoryTrackingInBackgroundProcessingPool
value:       -580863171
description: Total amount of memory (bytes) allocated in background processing pool (that is dedicated for backround merges, mutations and fetches). Note that this value may include a drift when the memory was allocated in a context of background processing pool and freed in other context or vice-versa. This happens naturally due to caches for tables indexes and doesn't indicate memory leaks.

Row 32:
───────
metric:      MemoryTrackingInBackgroundMoveProcessingPool
value:       0
description: Total amount of memory (bytes) allocated in background processing pool (that is dedicated for backround moves). Note that this value may include a drift when the memory was allocated in a context of background processing pool and freed in other context or vice-versa. This happens naturally due to caches for tables indexes and doesn't indicate memory leaks.

Row 33:
───────
metric:      MemoryTrackingInBackgroundSchedulePool
value:       -4461308831
description: Total amount of memory (bytes) allocated in background schedule pool (that is dedicated for bookkeeping tasks of Replicated tables).

...

56 rows in set. Elapsed: 0.003 sec.
```

Server version: 20.8.2.3.
{
    auto lock = getLock();
    auto initial_condition = initial_row_policy ? initial_row_policy->getCondition(database, table_name, type) : nullptr;
    return getAccess()->getRowPolicyCondition(database, table_name, type, initial_condition);
}
void Context::setInitialRowPolicy()
{
    auto lock = getLock();
    auto initial_user_id = getAccessControlManager().find<User>(client_info.initial_user);
    initial_row_policy = nullptr;
    if (initial_user_id)
        initial_row_policy = getAccessControlManager().getEnabledRowPolicies(*initial_user_id, {});
}
std::shared_ptr<const EnabledQuota> Context::getQuota() const
{
    return getAccess()->getQuota();
}
std::optional<QuotaUsage> Context::getQuotaUsage() const
{
    return getAccess()->getQuotaUsage();
}
void Context::setProfile(const String & profile_name)
{
    applySettingsChanges(*getAccessControlManager().getProfileSettings(profile_name));
}
const Scalars & Context::getScalars() const
{
    return scalars;
}
const Block & Context::getScalar(const String & name) const