title: Get item at specific offset of QMap
body: <p>I have a <code>QMap</code> that represents a database row. The items are indexed by column name:</p>
  
  <pre><code>QMap&lt;QString, QVariant&gt; mapOfItems_;
  </code></pre>
  
  <p>I then have a method to retrieve item by columnn name:</p>
  
  <pre><code>QVariant ImportDataSourceRow::byName( const QString&amp; name )
  {
      if(mapOfItems_.contains(name))
        return mapOfItems_.value(name);
      else
        throw NoSuchColumn();
  }
  </code></pre>
  
  <p>I would like to also implement method to get item by column index (<code>0</code> for first column):</p>
  
  <pre><code>QVariant ImportDataSourceRow::byIndex( size_t index )
  {
      // Now what?
  }
  </code></pre>
  
  <p>How can I get the value at offset <code>index</code> from the map? Is <code>QMap</code> even guaranteed to be ordered as I need it to be?</p>