**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`.

{
    if (in.eof())
        return false;
    updateDiagnosticInfo();
    
    
    
    bool have_default_columns = have_always_default_columns;
    ext.read_columns.assign(column_mapping->read_columns.size(), true);
    const auto delimiter = format_settings.csv.delimiter;
    for (size_t file_column = 0; file_column < column_mapping->column_indexes_for_input_fields.size(); ++file_column)
    {
        const auto & table_column = column_mapping->column_indexes_for_input_fields[file_column];
        const bool is_last_file_column = file_column + 1 == column_mapping->column_indexes_for_input_fields.size();
        if (table_column)
        {
            skipWhitespacesAndTabs(in);
            ext.read_columns[*table_column] = readField(*columns[*table_column], data_types[*table_column],
                serializations[*table_column], is_last_file_column);
            if (!ext.read_columns[*table_column])
                have_default_columns = true;