**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`.

column_mapping->read_columns.assign(header.columns(), false);
            do
            {
                String column_name;
                skipWhitespacesAndTabs(in);
                readCSVString(column_name, in, format_settings.csv);
                skipWhitespacesAndTabs(in);
                addInputColumn(column_name);
            }
            while (checkChar(format_settings.csv.delimiter, in));
            skipDelimiter(in, format_settings.csv.delimiter, true);
            for (auto read_column : column_mapping->read_columns)
            {
                if (!read_column)
                {
                    have_always_default_columns = true;
                    break;
                }
            }
            return;
        }
        else
            skipRow(in, format_settings.csv, num_columns);
    }
    else if (!column_mapping->is_set)
        setupAllColumnsByTableSchema();
}
bool CSVRowInputFormat::readRow(MutableColumns & columns, RowReadExtension & ext)