Call QHeaderView::initializeSections() to initialise QHeaderView

* Because many of QHeaderView's functions are annoyingly not virtual,
  we need some stub data available in QHeaderView even if it won't be
  used for anything much, like the number of sections.

qrenderdoc/Widgets/Extended/RDHeaderView.cpp

@@ -146,6 +146,8 @@ void RDHeaderView::cacheSections()
   if(m_pinnedColumns >= m_sections.count())
     m_pinnedWidth = m_pinnedColumns;
 
+  QHeaderView::initializeSections();
+
   QStyleOptionHeader opt;
   initStyleOption(&opt);