**Describe the bug**
Using `ALTER LIVE VIEW view REFRESH` results in an exception.

**How to reproduce**
* Connected to ClickHouse server version 20.8.1 revision 54438
* `CREATE TABLE` statements for all tables involved
```
clicktest :) SHOW CREATE table0

SHOW CREATE TABLE table0

┌─statement─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ CREATE TABLE default.table0
(
    `d` Date,
    `a` String,
    `b` UInt8,
    `x` String,
    `y` Int8
)
ENGINE = MergeTree()
ORDER BY d
SETTINGS index_granularity = 8192 │
└───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

1 rows in set. Elapsed: 0.006 sec.
```
* Queries to run that lead to unexpected result
```
ClickHouse client version 20.8.1.4447 (official build).
Connecting to localhost:9000 as user default.
Connected to ClickHouse server version 20.8.1 revision 54438.

clicktest :) SET allow_experimental_live_view=1

SET allow_experimental_live_view = 1

Ok.

0 rows in set. Elapsed: 0.003 sec.

clicktest :) CREATE LIVE VIEW live1 AS SELECT * FROM table0

CREATE LIVE VIEW live1 AS
SELECT *
FROM table0

Ok.

0 rows in set. Elapsed: 0.008 sec.

clicktest :) ALTER LIVE VIEW live1 REFRESH

ALTER LIVE VIEW live1
    REFRESH

Received exception from server (version 20.8.1):
Code: 49. DB::Exception: Received from localhost:9000. DB::Exception: RWLockImpl::getLock(): RWLock is already locked in exclusive mode.

0 rows in set. Elapsed: 0.005 sec.
```
**Expected behavior**
A clear and concise description of what you expected to happen.


block.updateHash(hash);
        
        block.insert({DataTypeUInt64().createColumnConst(
            block.rows(), getBlocksVersion() + 1)->convertToFullColumnIfConst(),
            std::make_shared<DataTypeUInt64>(),
            "_version"});
        new_blocks->push_back(block);
    }
    hash.get128(key.low, key.high);
    
    
    
    bool updated = false;
    {
        if (getBlocksHashKey() != key.toHexString())
        {
            if (new_blocks->empty())
            {
                new_blocks->push_back(getHeader());
            }
            new_blocks_metadata->hash = key.toHexString();
            new_blocks_metadata->version = getBlocksVersion() + 1;
            (*blocks_ptr) = new_blocks;
            (*blocks_metadata_ptr) = new_blocks_metadata;
            updated = true;
        }
    }
    return updated;
}
void StorageLiveView::checkTableCanBeDropped() const