One of our users just killed mutations produced by `ALTER MODIFY` queries on 21 servers. After that new alters on three servers stuck with:
```
Cannot execute alter metadata with version: 8 because another alter 7 must be executed before
```

However, there is no corresponding alter №7 in the replication queue and no undone mutations:
```
select * from system.mutations where is_done = 0
```

However, in the ZooKeeper, we have the correct state of metadata_version:
```
Row 13:
───────
name:           metadata_version
value:          7
czxid:          23078663291
mzxid:          29401964979
ctime:          2020-09-02 17:52:08
mtime:          2020-11-13 00:43:18
version:        7
cversion:       0
aversion:       0
ephemeralOwner: 0
dataLength:     1
numChildren:    0
pzxid:          23078663291
```
`SYSTEM RESTART REPLICA dbname.table_name` solves the issue, but it seems like` KILL MUTATION` in some cases can lead to unfinished alter.
log_pointer = last_entry_index + 1;
                for (size_t copied_entry_idx = 0, num_copied_entries = copied_entries.size(); copied_entry_idx < num_copied_entries; ++copied_entry_idx)
                {
                    String path_created = dynamic_cast<const Coordination::CreateResponse &>(*responses[copied_entry_idx]).path_created;
                    copied_entries[copied_entry_idx]->znode_name = path_created.substr(path_created.find_last_of('/') + 1);
                    std::optional<time_t> unused = false;
                    insertUnlocked(copied_entries[copied_entry_idx], unused, state_lock);
                }
                last_queue_update = time(nullptr);
            }
            catch (...)
            {
                tryLogCurrentException(log);
                
                
                std::terminate();
            }
            if (!copied_entries.empty())
            {
                LOG_DEBUG(log, "Pulled {} entries to queue.", copied_entries.size());
                merge_strategy_picker.refreshState();
            }
        }
        storage.background_executor.triggerTask();
    }
    return stat.version;
}
namespace
{
Names getPartNamesToMutate(