**Describe the bug**
When you set the setting `input_format_with_names_use_header` to `0`, `INSERT` does not actually insert rows.

**How to reproduce**
* Which ClickHouse server version to use: git master `a21fe0b492cbc8628126a3cd493b83e82abf9978`, checked out on 2021-03-31
* Which interface to use: the native command-line client
* Non-default settings, if any: `input_format_with_names_use_header` = `0`
* `CREATE TABLE` statements for all tables involved:
```sql
CREATE TABLE csvtest
(
    `t` String
)
ENGINE = MergeTree
ORDER BY t
```
* Sample data for all these tables
`test.csv`:
```csv
t
testdata1
testdata2
```
* Queries to run that lead to unexpected result:
```
% clickhouse-client --input_format_with_names_use_header 0 --query "INSERT INTO csvtest FORMAT CSVWithNames" < test.csv
```

**Expected behavior**
Two rows `('testdata1'), ('testdata2')` will be inserted to the table `csvtest`.

**Error message and/or stacktrace**
Nothing. It silently discards the input and inserts nothing to the table.

**Additional context**
It works as expected if you set `input_format_with_names_use_header` to `1`.

{
    const auto column_it = column_indexes_by_names.find(column_name);
    if (column_it == column_indexes_by_names.end())
    {
        if (format_settings.skip_unknown_fields)
        {
            column_mapping->column_indexes_for_input_fields.push_back(std::nullopt);
            return;
        }
        throw Exception(
                "Unknown field found in CSV header: '" + column_name + "' " +
                "at position " + std::to_string(column_mapping->column_indexes_for_input_fields.size()) +
                "\nSet the 'input_format_skip_unknown_fields' parameter explicitly to ignore and proceed",
                ErrorCodes::INCORRECT_DATA
        );
    }
    const auto column_index = column_it->second;
    if (column_mapping->read_columns[column_index])
        throw Exception("Duplicate field found while parsing CSV header: " + column_name, ErrorCodes::INCORRECT_DATA);
    column_mapping->read_columns[column_index] = true;
    column_mapping->column_indexes_for_input_fields.emplace_back(column_index);
}
static void skipEndOfLine(ReadBuffer & in)