(you don't have to strictly follow this form)

It seems that CH doesn't support  `FORMAT CustomSeparated` with http request
https://github.com/ClickHouse/ClickHouse/issues/12744#issuecomment-663738562

When I make a request with `format_custom_field_delimiter='^'`, I got an error
```
Code: 49, e.displayText() = DB::Exception: There is no checkpoint (version 20.1.2.4 (official build)) 
```
Bash script:
```
#!/bin/bash

find . -type f -name 'j.log' | while read f; do
  curl "http://localhost:8123
/?query=INSERT%20INTO%20mydb%20FORMAT%20CustomSeparated%20SETTINGS%20format_custom_escaping_rule%3D%27CSV%27%2C%20format_custom_field_delimiter%20%3D%20%27%5E%27" --data-binary "@${f}"
done
```
But all is OK, when I do it with client:
```
cat j.log |clickhouse-client  -q "INSERT into mydb FORMAT CustomSeparated SETTINGS format_custom_escaping_rule='CSV', format_custom_field_delimiter = '^'"
```


**How to reproduce**
* Which ClickHouse server version to use
 version 20.13.1.1 and github build `commit 6e34a0b71efc0e5af1cfb05b77a5e7b2568a2e49`
* Which interface to use, if matters
* Non-default settings, if any
* `CREATE TABLE` statements for all tables involved
```
CREATE TABLE mydb
(
	datetime  String,
	d1 String,
	d2 String
)
engine=MergeTree()
ORDER BY d1
SETTINGS index_granularity = 8192;
```
* Sample data for all these tables, use [clickhouse-obfuscator](https://github.com/ClickHouse/ClickHouse/blob/master/programs/obfuscator/Obfuscator.cpp#L42-L80) if necessary

j.log:
```
2021-Jan^d1^d2
```

* Queries to run that lead to unexpected result

**Expected behavior**
A clear and concise description of what you expected to happen.

**Error message and/or stacktrace**
If applicable, add screenshots to help explain your problem.

**Additional context**
Add any other context about the problem here.

{
    if (!checkpoint)
        throw DB::Exception("There is no checkpoint", ErrorCodes::LOGICAL_ERROR);
    checkStateCorrect();
    if (!checkpointInOwnMemory() || currentlyReadFromOwnMemory())
        return;     
    size_t bytes_to_append = pos - sub_buf.position();
    resizeOwnMemoryIfNecessary(bytes_to_append);
    memcpy(memory.data() + peeked_size, sub_buf.position(), bytes_to_append);
    sub_buf.position() = pos;
    peeked_size += bytes_to_append;
    BufferBase::set(memory.data(), peeked_size, peeked_size);
}
PeekableReadBuffer::~PeekableReadBuffer()
{
    if (!currentlyReadFromOwnMemory())
        sub_buf.position() = pos;
}
bool PeekableReadBuffer::hasUnreadData() const
{
    return peeked_size && pos != memory.data() + peeked_size;
}
}