**Describe the bug**
The ClickHouse client freezes when executing `ALTER TABLE` with `ADD COLUMN` and `MODIFY ORDER` on a table built using Replicated Versioned Collapsing Merge Tree engine.

**How to reproduce**
* ClickHouse client version 20.10.1.1.
Connecting to localhost:9000 as user default.
Connected to ClickHouse server version 20.10.1 revision 54440.

* `CREATE TABLE` statements
```
SHOW CREATE TABLE table0

┌─statement──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ CREATE TABLE default.table0
(
    `d` Date,
    `a` String,
    `b` UInt8,
    `x` String,
    `y` Int8,
    `version` UInt64,
    `sign` Int8 DEFAULT 1
)
ENGINE = ReplicatedVersionedCollapsingMergeTree('/clickhouse/tables/{shard}/table0', '{replica}', sign, version)
PARTITION BY y
ORDER BY d
SETTINGS index_granularity = 8192 │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

1 rows in set. Elapsed: 0.004 sec.
```

* Queries to run that lead to unexpected result
```
ALTER TABLE table0 ADD COLUMN order UInt32, MODIFY ORDER BY (d, order)
```
#include <Disks/StoragePolicy.h>
#include <Databases/IDatabase.h>
#include <Parsers/formatAST.h>
#include <Parsers/ASTDropQuery.h>
#include <Parsers/ASTOptimizeQuery.h>
#include <Parsers/ASTLiteral.h>
#include <Parsers/queryToString.h>
#include <Parsers/ASTCheckQuery.h>
#include <Parsers/ASTSetQuery.h>
#include <IO/ReadBufferFromString.h>
#include <IO/Operators.h>
#include <IO/ConnectionTimeouts.h>
#include <Interpreters/InterpreterAlterQuery.h>
#include <Interpreters/PartLog.h>
#include <Interpreters/Context.h>
#include <DataStreams/RemoteBlockInputStream.h>
#include <DataStreams/copyData.h>
#include <Poco/DirectoryIterator.h>
#include <ext/range.h>
#include <ext/scope_guard.h>
#include <ctime>
#include <thread>
#include <future>
#include <boost/algorithm/string/join.hpp>
namespace ProfileEvents
{
    extern const Event ReplicatedPartMerges;
    extern const Event ReplicatedPartMutations;
    extern const Event ReplicatedPartFailedFetches;
    extern const Event ReplicatedPartFetchesOfMerged;