**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.


DB::ErrorCodes::LOGICAL_ERROR);
        if (ast_select->list_of_selects->children.size() != 1)
            throw Exception("UNION is not supported for LIVE VIEW", ErrorCodes::QUERY_IS_NOT_SUPPORTED_IN_LIVE_VIEW);
        inner_subquery = ast_select->list_of_selects->children.at(0)->clone();
        return extractDependentTable(ast_select->list_of_selects->children.at(0), context, table_name, inner_subquery);
    }
    else
    {
        
        return StorageID("system", "one");
    }
}
MergeableBlocksPtr StorageLiveView::collectMergeableBlocks(const Context & context)
{
    ASTPtr mergeable_query = inner_query;
    if (inner_subquery)
        mergeable_query = inner_subquery;
    MergeableBlocksPtr new_mergeable_blocks = std::make_shared<MergeableBlocks>();
    BlocksPtrs new_blocks = std::make_shared<std::vector<BlocksPtr>>();
    BlocksPtr base_blocks = std::make_shared<Blocks>();
    InterpreterSelectQuery interpreter(mergeable_query->clone(), context, SelectQueryOptions(QueryProcessingStage::WithMergeableState), Names());
    auto view_mergeable_stream = std::make_shared<MaterializingBlockInputStream>(interpreter.execute().getInputStream());
    while (Block this_block = view_mergeable_stream->read())
        base_blocks->push_back(this_block);
    new_blocks->push_back(base_blocks);
    new_mergeable_blocks->blocks = new_blocks;
    new_mergeable_blocks->sample_block = view_mergeable_stream->getHeader();
    return new_mergeable_blocks;
}
Pipes StorageLiveView::blocksToPipes(BlocksPtrs blocks, Block & sample_block)