title: Why filterAcceptsRow when inheriting from QSortFilterProxyModel is not invoked?
body: <p>There is a class named customSortFilterProxyModel inheriting from QSortFilterProxyModel. And one protected function filterAcceptsRow is override.
  But, filterAcceptsRow is not called at all. what is the promblem?
  thanks.
  customSortFilterProxyModel.h</p>
  
  <pre><code>class customSortFilterProxyModel: public QSortFilterProxyModel
          {
             Q_OBJECT
  
          public:
              customSortFilterProxyModel(QObject *parent);
              ~customSortFilterProxyModel();
  
          protected:
             virtual bool filterAcceptsRow(int source_row, const QModelIndex &amp;source_parent) const override;   
          };
  
  //customSortFilterProxyModel.cpp
  customSortFilterProxyModel::customSortFilterProxyModel(QObject *parent)
  : QSortFilterProxyModel(parent)
  {
  }
  customSortFilterProxyModel::~customSortFilterProxyModel()
  {
  
  }
  bool customSortFilterProxyModel::filterAcceptsRow(int source_row, const QModelIndex &amp;source_parent) const
  {
     return true;
  }
  </code></pre>
  
  <p>Test code using this proxy model</p>
  
  <pre><code>    QStringListModel *newModel = new QStringListModel;
      QStringList strList;
      strList &lt;&lt; "1" &lt;&lt; "2" &lt;&lt; "3" &lt;&lt; "4";
  newModel-&gt;setStringList(strList);
      customSortFilterProxyModel   *m_customSortFilterProxyModel = new customSortFilterProxyModel(this);
         m_customSortFilterProxyModel-&gt;setSourceModel(newModel);
  </code></pre>